STABILITY OF HIGHWAY BRIDGES SUBJECT TO SCOUR Except where reference is made to the work of others, the work described in this thesis is my own or was done in collaboration with my advisory committee. This thesis does not include proprietary or classified information. _______________________ James Nickolas Walker Certificate of Approval: _____________________ _____________________ Mary L. Hughes G. Ed Ramey, Chair Assistant Professor Professor Emeritus Civil Engineering Civil Engineering _____________________ _____________________ Robert W. Barnes George T. Flowers Associate Professor Interim Dean Civil Engineering Graduate School STABILITY OF HIGHWAY BRIDGES SUBJECT TO SCOUR James Nickolas Walker A Thesis Submitted to the Graduate Faculty of Auburn University in Partial Fulfillment of the Requirements for the Degree of Masters of Science Auburn, Alabama December 19, 2008 iii STABILITY OF HIGHWAY BRIDGES SUBJECT TO SCOUR James Nickolas Walker Permission is granted to Auburn University to make copies of this thesis at its discretion, upon requests of individuals or institutions and at their expense. The author reserves all publication rights. _____________________ Signature of Author _____________________ Date of Graduation iv THESIS ABSTRACT STABILITY OF HIGHWAY BRIDGES SUBJECT TO SCOUR James Nickolas Walker Master of Science, December 19, 2008 (B.C.E., Auburn University, 2006) 238 Typed Pages Directed by G. Ed Ramey A common design/construction procedure for highway bridges in Alabama is the use of steel HP piles driven into a firm stratum with a length above ground/water up to the level of a concrete bent cap which supports the bridge superstructure. The use of 3, 4, 5, or 6 such piles in a row with the two end piles battered are very common bridge pile bents. The bents are sometimes encased in concrete from the bent cap down to three feet below ground level and sometimes the piles are X-braced in the plane of the piles for lateral support. The objectives of the Phase I research work were to identify the primary parameters of importance in assessing the adequacy of bridge pile bents for extreme scour events, and to identify the best approach to follow in developing a simple ?screening tool?, to check the adequacy. The objective of the Phase II research work was to develop a simple ?screening tool? and a user?s guide v explaining the proper use of the tool, for use in evaluating the structural stability of simple pile bent-supported bridges in an extreme scour event. The objectives of this Phase III research work were to expand, refine, and automate the ?screening tool? developed in Phase II work. This thesis presents the expansions, refinements, and Tier-2 screenings added to the original ?screening tool?. The computer automation of the refined/2nd edition ?screening tool? presented in this thesis is presented and discussed in a sister Phase III thesis. vi ACKNOWLEDGEMENTS I would first like to thank Dr. Ramey for giving me this chance to work with him on this project and earn my Masters Degree. I am grateful for all his guidance and help throughout the project. I would also like to thank Nicole Donnee and Dr. Hughes for their help and cooperation on the project. This thesis was prepared under cooperative agreement between the Alabama Department of Transportation (ALDOT) and the Highway Research Center (HRC) at Auburn University. I would like to thank the ALDOT and HRC for their sponsorship and support of the work. I am also thankful for the assistance and guidance of several ALDOT engineers during the execution of the research work. Specifically, thanks are due to George Conner, Eric Christie, Randall Mullins, and Robert Fulton of the ALDOT. Lastly, I would like to thank my family and friends for their support; most importantly my mother Julie for her encouragement and inspiration, and also Stephanie for her patience and encouragement. vii Style used: Chicago Manual Style Computer software used: Microsoft Word, Microsoft Excel, Microsoft Paint, GTSTRUDL viii TABLE OF CONTENTS LIST OF TABLES................................................................................................ xii LIST OF FIGURES.............................................................................................. xx CHAPTER 1: INTRODUCTION............................................................................1 Statement of Problem ................................................................................1 Research Objectives..................................................................................2 Work Plan ..................................................................................................3 CHAPTER 2: ADDITIONAL ?ST? LOAD AND SCOUR CONDITIONS, LOAD LEVELS, SENSITIVITY OF PUSHOVER LOAD TO BENT CAP STIFFNESS, AND EFFECTS OF CONTINUOUS-SPAN SUPERSTRUCTURES...................................................................6 General ......................................................................................................6 Sensitivity of Pushover Load to Bent Cap Size/Stiffness ...........................7 Additional Axial Pile Load Due to Flood Water Loading...........................12 Effect of Continuous-Span Superstructures on Bridge/Bent Pushover ....15 Effect of Continuous-Span Superstructures on Bent Pile Buckling ..........21 Pushover Loads for Additional P-load and Scour Levels .........................24 Pushover Loads for Unsymmetric P-load Distribution..............................51 Pushover Loads for Variable Scour Distribution.......................................65 ix Pushover Loads for Unsymmetric P-load and Variable Scour Distributions ..................................................................................86 Bent Pushover Failure in Terms of Critical Scour Level...........................95 Check Upstream Bent Pile for Beam-Column Failure from Debris Raft Loading.......................................................................................104 Effect of Height of Debris Raft Loading on Bent Pushover ....................117 Additional Expansions of Applicability of the Tier-1 Screening Tool.......125 Closure ..................................................................................................126 CHAPTER 3: DETERMINING BRIDGE/BENT MAXIMUM APPLIED LOADS........................................................................................127 General ..................................................................................................127 Determining Maximum Applied Dead Load............................................129 Determining Maximum Applied Live Load..............................................130 Example PBent Max Applied Determinations ..................................................133 CHAPTER 4: REFINED ?ST? AND TIER-2 SCREENINGS..............................140 General ..................................................................................................140 Refined/2nd Edition ?ST?.........................................................................141 Second Tier/Tier-2 Screening ................................................................153 Pile Plunging Evaluation 2nd Tier Screening ...............................153 Pile Plunging Evaluation 2nd Tier Screening ...............................154 Bent Pushover Evaluation 2nd Tier Screening.............................157 Closure ..................................................................................................157 CHAPTER 5: EXAMPLE APPLICATIONS OF THE TIER-2 ?ST?.....................161 x General ..................................................................................................161 Bent/Site Conditions to Check For Need/Applicability of the ?ST?..........162 Example Applications for Tier-2 Pile Plunging Failure Check ................163 Example Applications for Tier-2 Buckling Failure Check........................173 Example Applications for Tier-2 Bent Pushover Failure Check..............177 Example Application for Bent Upstream Pile Beam-Column Failure Check..........................................................................................188 Closure ..................................................................................................190 CHAPTER 6: CONCLUSIONS AND RECOMMENDATIONS ..........................191 General ..................................................................................................191 Conclusions ...........................................................................................192 Additional Pile Axial P-load Due to Flood Water Lateral Loading............................................................................192 Effect of Continuous Spans on Bent Pushover ...........................193 Effect of Continuous Spans on Bent Pile Buckling......................193 Bent Pushover Loads for Smaller P-load Levels.........................194 Pushover Loads for Unsymmetric P-load Distribution.................194 Pushover Loads for Variable Scour Distribution .........................196 Effect of Vertical Location of Debris Raft on Bent Pushover.......196 Bent Upstream Pile as a Beam-Column .....................................197 Recommendations.................................................................................198 REFERENCES..................................................................................................201 xi APPENDIX A: EXAMPLE GTSTRUDL INPUT CODE FOR PUSHOVER ANALYSIS FOR VARIOUS BENT CONFIGURATIONS.............203 xii LIST OF TABLES Table 2.1. Ft for Unbraced 3-Pile and 4-Pile Bridge Bents for Varying Values of Bent Cap Igross - HP10X42 Piles and P=100k.................................................8 Table 2.2. PCR and PMAX ALLOWED for Bent Piles Supporting Continuous Span Bridge ......................................................................................................23 Table 2.3a. Pushover Load, Ft, for Unbraced 3-Pile and 4-Pile Bridge Bents with HP10X42 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4 for Varying Values of P-Load and ?H+S?...................................................29 Table 2.3b. Pushover Load, Ft, for Unbraced 3-Pile and 4-Pile Bridge Bents with HP12X53 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4 for Varying Values of P-Load and ?H+S?...................................................30 Table 2.4a. Pushover Load, Ft, for Unbraced 5-Pile and 6-Pile Bridge Bents with HP10X42 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4 for Varying Values of P-Load and ?H+S?...................................................31 Table 2.4b. Pushover Load, Ft, for Unbraced 5-Pile and 6-Pile Bridge Bents with HP12X53 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4 for Symmetric Distribution of Varying Values of P-Load and ?H+S?..........32 xiii Table 2.5a. Pushover Load, Ft, for X-Braced 3-Pile and 4-Pile Bridge Bents with HP10X42 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4 for Symmetric Distribution of Varying Values of P-Load and ?H+S?..........33 Table 2.5b. Pushover Load, Ft, for X-Braced 3-Pile and 4-Pile Bridge Bents with HP12X53 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4 for Symmetric Distribution of Varying Values of P-Load and ?H+S?..........34 Table 2.6a. Pushover Load, Ft, for Single Story X-Braced 5-Pile and 6-Pile Bridge Bents with HP10X42 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4 for Symmetric Distribution of Varying Values of P-Load and ?H+S? .................................................................................................35 Table 2.6b. Pushover Load, Ft, for Single Story X-Braced 5-Pile and 6-Pile Bridge Bents with HP12X53 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4 for Symmetric Distribution of Varying Values of P-Load and ?H+S? .................................................................................................36 Table 2.7a. Pushover Load, Ft, for 2- Story X-Braced 3-Pile and 4-Pile Bridge Bents with HP10X42 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4 for Symmetric Distribution of Varying Values of P-Load and ?H+S? ........................................................................................................45 Table 2.7b. Pushover Load, Ft, for 2- Story X-Braced 3-Pile and 4-Pile Bridge Bents with HP12X53 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4 for Symmetric Distribution of Varying Values of P-Load and ?H+S? ........................................................................................................46 xiv Table 2.8a. Pushover Load, Ft, for 2- Story X-Braced 5-Pile and 6-Pile Bridge Bents with HP10X42 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4 for Symmetric Distribution of Varying Values of P-Load and ?H+S? ........................................................................................................47 Table 2.8b. Pushover Load, Ft, for 2- Story X-Braced 5-Pile and 6-Pile Bridge Bents with HP12X53 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4 for Symmetric Distribution of Varying Values of P-Load and ?H+S? ........................................................................................................48 Table 2.9a. Pushover Load, Ft, for Double X-Braced 1-Story and 2-Story 6-Pile Bridge Bents with HP10X42 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric P-Loads and Scour ...........................................................49 Table 2.9b. Pushover Load, Ft, for Double X-Braced 1-Story and 2-Story 6-Pile Bridge Bents with HP12X53 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric P-Loads and Scour ...........................................................50 Table 2.10a. Pushover Load, Ft, for Unbraced 3-Pile and 4-Pile Bridge Bents with HP10X42 Piles and Concrete Cap with Igross = 41,470 in4 for Unsymmetric P-Loadings and Varying Values of ?H+S? ...........................55 Table 2.10b. Pushover Load, Ft, for Unbraced 3-Pile and 4-Pile Bridge Bents with HP12X53 Piles and Concrete Cap with Igross = 41,470 in4 for Unsymmetric P-Loadings and Varying Values of ?H+S? ...........................56 Table 2.11a. Pushover Load, Ft, for Single Story X-Braced 3-Pile and 4-Pile Bridge Bents with HP10X42 Piles and Concrete Cap with Igross = 41,470 in4 for Unsymmetric P-Loadings and Varying Values of ?H+S? ......................57 xv Table 2.11b. Pushover Load, Ft, for Single Story X-Braced 3-Pile and 4-Pile Bridge Bents with HP12X53 Piles and Concrete Cap with Igross = 41,470 in4 for Unsymmetric P-Loadings and Varying Values of ?H+S? ......................58 Table 2.12a. Pushover Load, Ft, for 2-Story X-Braced 3-Pile and 4-Pile Bridge Bents with HP10X42 Piles and Concrete Cap with Igross = 41,470 in4 for Varying Values of ?H+S? and Unsymmetric P-Loadings ...........................63 Table 2.12b. Pushover Load, Ft, for 2-Story X-Braced 3-Pile and 4-Pile Bridge Bents with HP12X53 Piles and Concrete Cap with Igross = 41,470 in4 for Varying Values of ?H+S? and Unsymmetric P-Loadings ...........................64 Table 2.13a. Pushover Load, Ft, for Unbraced 3-Pile and 4-Pile Bridge Bents with HP10X42 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4 for Varying Values of P-Load and for Variable Scour and ?H+S? Distributions .............................................................................................70 Table 2.13b. Pushover Load, Ft, for Unbraced 3-Pile and 4-Pile Bridge Bents with HP12X53 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4 for Varying Values of P-Load and for Variable Scour and ?H+S? Distributions .............................................................................................71 Table 2.14a. Pushover Load, Ft, for Unbraced 5-Pile and 6-Pile Bridge Bents with HP10X42 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric P-Loads and Variable Scour and ?H+S? Distributions...............................72 Table 2.14b. Pushover Load, Ft, for Unbraced 5-Pile and 6-Pile Bridge Bents with HP12X53 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric P-Loads and Variable Scour and ?H+S? Distributions...............................73 xvi Table 2.15a. Pushover Load, Ft, for Single Story X-Braced 3-Pile and 4-Pile Bridge Bents with HP10X42 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4 for Symmetric Distribution of Varying Values of P-Load and ?H+S? for Variable Scour Distribution.................................................74 Table 2.15b. Pushover Load, Ft, for Single Story X-Braced 3-Pile and 4-Pile Bridge Bents with HP12X53 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4 for Varying Values of P-Load and for Variable Scour and ?H+S? Distributions....................................................................................75 Table 2.16a. Pushover Load, Ft, for Single Story X-Braced 5-Pile and 6-Pile Bridge Bents with HP10X42 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric P-Loads and Variable Scour and ?H+S? Distributions........76 Table 2.16b. Pushover Load, Ft, for Single Story X-Braced 5-Pile and 6-Pile Bridge Bents with HP12X53 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric P-Loads and Variable Scour and ?H+S? Distributions........77 Table 2.17a. Pushover Load, Ft, for 2-Story X-Braced 3-Pile and 4-Pile Bridge Bents with HP10X42 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric P-Loadings and Variable Scour and ?H+S? Distributions ........80 Table 2.17b. Pushover Load, Ft, for 2-Story X-Braced 3-Pile and 4-Pile Bridge Bents with HP12X53 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric P-Loadings and Variable Scour and ?H+S? Distributions ........81 Table 2.18a. Pushover Load, Ft, for 2-Story X-Braced 5-Pile and 6-Pile Bridge Bents with HP10X42 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric P-Loads and Variable Scour and ?H+S? Distributions .............82 xvii Table 2.18b. Pushover Load, Ft, for 2-Story X-Braced 5-Pile and 6-Pile Bridge Bents with HP12X53 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric P-Loads and Variable Scour and ?H+S? Distributions .............83 Table 2.19a. Pushover Load, Ft, for Double X-Braced 1-Story and 2-Story 6-Pile Bridge Bents with HP10X42 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric P-Loads and Variable Scour and ?H+S? Distributions........84 Table 2.19b. Pushover Load, Ft, for Double X-Braced 1-Story and 2-Story 6-Pile Bridge Bents with HP12X53 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric P-Loads and Variable Scour and ?H+S? Distributions........85 Table 2.20a. Pushover Load, Ft, for Unbraced 3-Pile and 4-Pile Bridge Bents with HP10X42 Piles and Concrete Cap with Igross = 41,470 in4 for Unsymmetric P-Loadings and Variable Scour and ?H+S? Distributions ....88 Table 2.20b. Pushover Load, Ft, for Unbraced 3-Pile and 4-Pile Bridge Bents with HP12X53 Piles and Concrete Cap with Igross = 41,470 in4 for Unsymmetric P-Loadings and Variable Scour and ?H+S? Distributions ....89 Table 2.21a. Pushover Load, Ft, for Single Story X-Braced 3-Pile and 4-Pile Bridge Bents with HP10X42 Piles and Concrete Cap with Igross = 41,470 in4 for Unsymmetric P-Loadings and for Variable Scour and ?H+S? Distributions .............................................................................................90 Table 2.21b. Pushover Load, Ft, for Single Story X-Braced 3-Pile and 4-Pile Bridge Bents with HP12X53 Piles and Concrete Cap with Igross = 41,470 in4 for Unsymmetric P-Loadings and for Variable Scour and ?H+S? Distributions .............................................................................................91 xviii Table 2.22a. Pushover Load, Ft, for 2- Story X-Braced 3-Pile and 4-Pile Bridge Bents with HP10X42 Piles and Concrete Cap with Igross = 41,470 in4 for Unsymmetric P-Loadings and for Variable Scour and ?H+S? Distributions .............................................................................................93 Table 2.22b. Pushover Load, Ft, for 2- Story X-Braced 3-Pile and 4-Pile Bridge Bents with HP12X53 Piles and Concrete Cap with Igross = 41,470 in4 for Unsymmetric P-Loadings and for Variable Scour and ?H+S? Distributions .............................................................................................94 Table 2.23a. Critical Uniform Scour, SCR, of HP10X42 3, 4, 5, 6-Pile Bents without X-Bracing to Resist Ft max design = 12.15k (includes a FS = 1.25) ...............96 Table 2.23b. Critical Uniform Scour, SCR, of HP12X53 3, 4, 5, 6-Pile Bents without X-Bracing to Resist Ft max design = 12.15k (includes a FS = 1.25) ...............97 Table 2.24a. Critical Uniform Scour, SCR, of HP10X42 3, 4, 5, 6-Pile Bents with X-Bracing to Resist Ft max design = 12.15k (includes a FS = 1.25) ...............98 Table 2.24b. Critical Uniform Scour, SCR, of HP12X53 3, 4, 5, 6-Pile Bents with X-Bracing to Resist Ft max design = 12.15k (includes a FS = 1.25) ...............99 Table 2.25a. Critical Nonuniform Scour, SCR, of HP10X42 3, 4, 5, 6-Pile Bents without X-Bracing to Resist Ft max design = 12.15k (includes a FS = 1.25)............................................................................100 Table 2.25b. Critical Nonuniform Scour, SCR, of HP12X53 3, 4, 5, 6-Pile Bents without X-Bracing to Resist Ft max design = 12.15k (includes a FS = 1.25)............................................................................101 xix Table 2.26a. Critical Nonuniform Scour, SCR, of HP10X42 3, 4, 5, 6-Pile Bents with X-Bracing to Resist Ft max design = 12.15k (includes a FS = 1.25) .............102 Table 2.26b. Critical Nonuniform Scour, SCR, of HP12X53 3, 4, 5, 6-Pile Bents with X-Bracing to Resist Ft max design = 12.15k (includes a FS = 1.25) .............103 Table 2.27. Upstream Pile Beam-Column Failure for Lower Elevation Debris Raft with Ft = 9.72k and H = 13 ft Unbraced Bent with HP10X42 Piles .............112 Table 2.28. Pushover Load, Ft, at High or Low Position for 2- Story X-Braced 3- Pile and 4-Pile Bridge Bents of Height H = 21 ft with HP10X42 Piles and Concrete Bent Cap with Igross = 41,470 in4 for Symmetric P-Loads and Uniform Scour........................................................................................120 Table 2.29. Pushover Load, Ft, at Low Position for 2-Story X-Braced 3-Pile Bent of Height H = 21 ft with HP10X42 Piles for Various Values of Horizontal Brace (HB) Stiffnesses...........................................................................124 Table 3.1. Design Traffic Lanes (8)..................................................................128 Table 3.2. Bridge Girder Maximum Reactions for SS and Equal Span Continuous Bridges Under Uniform Loads.............................................129 xx LIST OF FIGURES Fig. 2.1. Qualitative Lateral Load Induced Bent Deformations.............................7 Fig. 2.2. Pushover Load vs. Bent Cap Igross for Unbraced 3- and 4-Pile Bents (HP10X42 Piles) and P = 100k ......................................................................9 Fig. 2.3. Stiffness and Relative Stiffness Parameters for Typical 3-Pile Bent ....11 Fig. 2.4. X-Braced Bent Qualitative Lateral Load-Deformation Behavior ...........11 Fig. 2.5. Maximum Pile Load for Checking Pile Plunging and Buckling .............12 Fig. 2.6. Maximum Additional Axial Pile Load, ?Pmax, Due to Ffw Load ..............14 Fig. 2.7. Lateral Flexural Stiffness of Bridge Deck System vs. Support Pile Bent System.....................................................................................................17 Fig. 2.8. Typical Pushover/Lateral Stiffness Curves for Unbraced and X-Braced Pile Bents (from Phase II Research)........................................................18 Fig. 2.9. 2-Span SS Bridge ................................................................................19 Fig. 2.10. Multi-SpanBridge with Many Rigid SS Spans.....................................19 Fig. 2.11. Multi-Span Bridge Composed of 2-Span Continuous Segments........19 Fig. 2.12. Maximum Bent Forces for Continuous Span Bridges.........................20 Fig. 2.13. FBent Max on 2-Span Continuous Bridge when Ft is Applied at Bent Where Superstructure has Continuity ......................................................21 xxi Fig. 2.14. Pile Buckling Modes and Equations for Bents Supporting Continuous Bridges.....................................................................................................22 Fig. 2.15. Pushover Load vs. Bent Height Plus Scour for Unbraced 3- and 4-Pile Bents (HP10X42 Piles) with P-Loads of 60k, 80k, 100k, 120k, 140k, and 160k..........................................................................................................37 Fig. 2.16. Pushover Load vs. Bent Height Plus Scour for Unbraced 3- and 4-Pile Bents (HP12X53 Piles) with P-Loads of 60k, 80k, 100k, 120k, 140k, and 160k..........................................................................................................38 Fig. 2.17. Pushover Load vs. Bent Height Plus Scour for Single Story X-Braced 3- and 4-Pile Bents (HP10X42 Piles) with P-Loads of 60k and 160k............39 Fig. 2.18. Pushover Load vs. Bent Height Plus Scour for Single Story X-Braced 3- and 4-Pile Bents (HP12X53 Piles) with P-Loads of 60k and 160k............40 Fig. 2.19a. GTSTRUDL Pushover Analysis Results for 13 ft Tall Non X-Braced HP10X42 Pile Bents Subject to Scour.........................................................41 Fig. 2.19b. GTSTRUDL Pushover Analysis Results for 13 ft Tall Non X-Braced HP10X42 Pile Bents Subject to Scour (cont?d)............................................42 Fig. 2.20. Pushover Load (Ft) vs. Bent Height Plus Scour (H+S) for 13 ft Tall Unbraced Bents with 6,5,4,3-Piles of HP10X42 and P = 100k.....................43 Fig. 2.21. Pushover Force vs. Scour (H+S) for 5-Pile Bent with H=10?, HP10X42, and P = 60k ..............................................................................................44 Fig. 2.22. 3-Pile Bent P-load Distributions..........................................................52 Fig. 2.23. 4-Pile Bent P-load Distributions..........................................................52 Fig. 2.24. Symmetric and Nonsymmetric P-load Distributions ...........................53 xxii Fig. 2.25. Unsymmetric P-load Levels and Distributions Used in Phase III Work ........................................................................................................53 Fig. 2.26. Pushover Load vs. Bent Height Plus Scour for Unbraced 3- and 4-Pile Bents (HP10X42 Piles) with Sym. and Unsym. P-Loads.............................59 Fig. 2.27. Pushover Load vs. Bent Height Plus Scour for Unbraced 3- and 4-Pile Bents (HP12X53 Piles) with Sym. and Unsym. P-Loads.............................60 Fig. 2.28. Pushover Load vs. Bent Height Plus Scour for Single Story X-Braced 3- and 4-Pile Bents (HP10X42 Piles) with Sym. and Unsym. P-Loads........61 Fig. 2.29. Pushover Load vs. Bent Height Plus Scour for Single Story X-Braced 3- and 4-Pile Bents (HP12X53 Piles) with Sym. and Unsym. P-Loads........62 Fig. 2.30. Forms of Scour in Rivers: a) Lateral Shift of a Stream Caused by Bank Erosion and Deposition; b) Normal Bottom Scour During Floods; c) Accelerated Scour Caused by a Bridge Pier. [From Sowers, 1962]........67 Fig. 2.31. Assumed Scour Distributions Profile ..................................................67 Fig. 2.32. Example Problem Illustrating the Effect of Scour Distribution on Bent Buckling Loads.........................................................................................68 Fig. 2.33. Pushover Load vs. Bent Height Plus Scour for Unbraced 3- and 4-Pile Bents (HP10X42 Piles) with Uniform and Variable Scour............................78 Fig. 2.34. Pushover Load vs. Bent Height Plus Scour for X-Braced 3- and 4-Pile Bents (HP10X42 Piles) with Uniform and Variable Scour............................79 Fig. 2.35. Pushover Load vs. Bent Height Plus Scour for Unbraced and X- Braced 3-Pile Bents (HP10X42 Piles) with Uniform P-Load and Scour and with Unsym. P-Load and Variable Scour .................................................92 xxiii Fig. 2.36. Maximum Height Unbraced Bent Showing Two HWL and Ft Locations................................................................................................106 Fig. 2.37. Upstream Pile, P1, Mmax Values for Pinned-End Condition..............106 Fig. 2.38. Upstream Pile, P1, Mmax Values for Fixed-End Condition ................107 Fig. 2.39. X-Braced Bent with Ft-Load at Level of Horizontal Brace.................108 Fig. 2.40. Checking Upstream Pile of Maximum Height Unbraced Bent as a Beam-Column........................................................................................110 Fig. 2.41. Interaction Diagram of Axial Pfailure vs. S for the Upstream Pile for Unbraced Bents with H=13 ft and HP10X42 Piles.....................................113 Fig. 2.42. Checking Adequacy of Bent Upstream Pile as a Beam-Column......116 Fig. 2.43. Two-Story X-Braced 3-Pile Bent with Horizontal Flood Water Load, Ft, Applied at Bottom of Cap or Location of Horizontal Strut in GTSTRUDL Pushover Analysis .................................................................................119 Fig. 2.44. Unbraced, 1-Story X-Braced, and 2-Story X-Braced Bent Deformations..........................................................................................121 Fig. 2.45. GTSTRUDL Generated Deformations of 3-Pile Bent from Ft Loadings ................................................................................................122 Fig. 2.46. GTSTRUDL Generated Deformations of 4-Pile Bent from Ft Loadings ................................................................................................123 Fig. 3.1. Live Load to Determine PLL Bent Max Applied.............................................129 Fig. 3.2. Girder Line Loading to Determine PLL Pile Max Applied..............................132 Fig. 3.3. AASHTO H and HS Lane Loading .....................................................132 xxiv Fig. 3.4. 34? Span SS Bridge with 7? Deck, AASHTO Type II Girders (4 Girders at 8? Spacing), Jersey Barriers, 4-Pile Bents with 2.5? x 2.5? Caps.........133 Fig. 3.5. Pushover Load Case I........................................................................135 Fig. 3.6. Pushover Load Case II.......................................................................136 Fig. 3.7. Unsymmetric P-Loading for 4-Pile Bents............................................136 Fig. 3.8. 34? Span SS Bridge with 7? Deck, AASHTO Type II Girders (3 Girders at 8? Spacing), Jersey Barriers, 3-Pile Bents with 2.5? x 2.5? Caps.........137 Fig. 3.9. Pushover Load Case I........................................................................138 Fig. 3.10. Pushover Load Case II.....................................................................139 Fig. 3.11. Unsymmetric P-Loading for 3-Pile Bents..........................................139 Fig. 4.1. Refined Screening Tool Flowchart for Assessing Pile Bent Adequacy During an Extreme Flood/Scour Event...................................................143 Fig. 4.2. Enlargement of Preliminary Evaluation Module..................................144 Fig. 4.3. Enlargement of Kick-Out and Plunging Evaluation Module................145 Fig. 4.4. Enlargement of Refined Buckling Evaluation Module.........................147 Fig. 4.5a. Typical ALDOT X-Braced Pile Bent Geometry.................................148 Fig. 4.5b. Transverse Buckling Modes and Equations for X-Braced Bents......149 Fig. 4.6. Enlargement of the Bent Pushover Evaluation Module ......................150 Fig. 4.7. Enlargement of Upstream Pile Beam-Column Evaluation Module .....152 Fig. 4.8a. Tier-2/2A Screening for Pile Plunging Adequacy Assessment.........155 Fig. 4.8b. Tier-2/2B Screening for Pile Plunging Adequacy Assessment.........156 Fig. 4.9a. Tier-2/4A Screening for Bent Pushover Adequacy Assessment ......158 Fig. 4.9b. Tier-2/4B Screening for Bent Pushover Adequacy Assessment ......159 xxv Fig. 5.1. Example Problem 1 for Kick-Out and Plunging ..................................164 Fig. 5.2. Example Problem 1 for Kick-Out and Plunging (Continued)...............165 Fig. 5.3. Example Problem 1 for Kick-Out and Plunging (Continued)...............166 Fig. 5.4. Example Problem 2 for Plunging........................................................167 Fig. 5.5. Example Problem 2 for Plunging (Continued) ....................................168 Fig. 5.6. Example Problem 2 for Plunging (Continued) ....................................169 Fig. 5.7. Example Problem 2 for Plunging (Continued) ....................................170 Fig. 5.8. Example Problem 2 for Plunging (Continued) ....................................171 Fig. 5.9. Example Problem 2 for Plunging (Continued) ....................................172 Fig. 5.10. Example Problem 3 for Buckling ......................................................174 Fig. 5.11. Example Problem 4 for Buckling ......................................................175 Fig. 5.12. Example Problem 5 for Buckling ......................................................176 Fig. 5.13. Example Problem 6 for Pushover.....................................................178 Fig. 5.14. Example Problem 6 for Pushover (Continued).................................179 Fig. 5.15. Example Problem 7 for Pushover.....................................................180 Fig. 5.16. Example Problem 7 for Pushover (Continued).................................181 Fig. 5.17. Example Problem 8 for Pushover.....................................................182 Fig. 5.18. Example Problem 8 for Pushover (Continued).................................183 Fig. 5.19. Example Problem 9 for Pushover.....................................................184 Fig. 5.20. Example Problem 9 for Pushover (Continued).................................185 Fig. 5.21. Example Problem 9 for Pushover (Continued).................................186 Fig. 5.22. Example Problem 9 for Pushover (Continued).................................187 Fig. 5.23. Example Problem 10 for Beam-Column...........................................189 1 CHAPTER 1: INTRODUCTION 1.1 Statement of Problem The Alabama Department of Transportation (ALDOT) is currently performing an assessment of the scour susceptibility of its bridges, and a part of this assessment requires an evaluation of the structural stability of these bridges for an estimated flood/scour event. Because of the large number of bridges in the state subject to flood/scour events, and because structural stability analyses of each bridge represent a considerable effort in time and money, there is a compelling need to develop a simple ?screening tool? which can be used, along with the scour analyses, to efficiently assess the susceptibility of these bridges to scour. Phases I and II of the research toward this end have already been completed. It was determined in Phase I that it was indeed technically feasible to develop such a ?screening tool?, the primary parameters on which the scour susceptibility depend were identified, and it was verified that these parameters were in ALDOT?s databases or could be estimated. In Phase II, a ?screening tool? (ST) was developed to assess the adequacy of bridge pile bents for an estimated flood/scour event, and a Users Guide was developed to assist engineers in using the ?screening tool?. 2 1.2 Research Objectives The objectives of this Phase III research were to enhance, simplify, expand the scope of applicability of the ?ST? (screening tool), to develop and incorporate Tier-2 screenings for bents that do not pass safely through the ?ST?, and to automate the ?ST? developed in Phase II. More specifically, the objectives of the Phase III work were as follows: 1. Work with ALDOT maintenance engineers performing bridge pile bent evaluations for adequacy during estimated extreme flood/scour events and identify how the ?screening tool? can be simplified, enhanced, and expanded in scope of applicability to make it more user-friendly and helpful to ALDOT engineers. 2. Work with ALDOT engineers to determine if there are minimal changes that can be made in the ?screening tool? that would allow significant expansion of the scope of applicability of the ?screening tool?. If there are, then make these changes. 3. Determine, where feasible, follow-up assessment procedures for those bents that do not pass through the ?screening tool? with an evaluation of ?the bent is safe from plunging (buckling, push-over)?. More specifically, identify the appropriate follow-up checking procedures for those bents where the ?screening tool? indicates that the ?bent should be looked at more closely for possible plunging (buckling, push-over) failure?. This will constitute a second tier of screening. 3 4. Work with ALDOT engineers to automate the ?screening tool? as it currently exists. As simplifications, enhancements, and expansions of the ?screening tool? are identified and made, it should be very easy to incorporate these into the automated version of the ?screening tool?. 1.3 Work Plan A brief work plan followed to accomplish the research objectives cited above is given in the work tasks below. 1. Work with ALDOT engineers in the bridge maintenance section to identify problem areas with the ?screening tool? (ST) and areas where the ST is difficult to apply and/or where parameters needed by the ST are not readily available, and make appropriate modification in the ST to overcome these problems and render the ST more user-friendly and helpful. 2. Work with ALDOT engineers to identify bounding cases for other bents used by the ALDOT for which the ST may be applicable in order that these bounding cases may be used to assess the adequacy of these other bents. Also, for these other bents, determine what changes or additional analyses must be made to extend the scope of application of the ST. If the changes in the ST can reasonably be made, then make these changes. 3. Identify what additional checking, analyses, and input data are needed 4 for bents for which the ST indicates ?check more closely for possible pile/bent plunging failure?. 4. Identify what additional checking, analyses, and input data are needed for bents for which the ST indicates ?check more closely for possible pile/bent buckling failure?. 5. Identify what additional checking, analyses, and input data are needed for bents for which the ST indicates ?check more closely for possible bent push-over failure?. 6. Develop a second tier ?screening tool? which includes the checks identified in Work Tasks 3, 4 and 5 above. Discuss with ALDOT engineers whether this second tier of screening should be incorporated into the present ST so that there is just one ST, or make a second ST which is used only for those bents which do not safely pass through the present ST. 7. Prepare and conduct a training program on the second tier ?screening tool? described in Task 6 above. 8. Work with ALDOT engineers to automate the ST for simple computer evaluation of the adequacy of bridge pile bents for estimated extreme flood/scour events. The automated ST will be a stand-alone computer 5 program system wherein ALDOT engineers input bridge/site parameter values and the program executes the ST evaluations and outputs intermediate and final results in a format appropriate for filing for record in the bridge?s file folder for future reference if needed. The automated computer program should allow the user to change one or more input parameter values and generate a new evaluation without having to re- input the other bridge/site parameters. 9. Prepare and conduct a training program on the automated ST described in Task 8 above. 10. Prepare Phase III Final Report. 6 CHAPTER 2: ADDITIONAL ?ST? LOAD AND SCOUR CONDITIONS, LOAD LEVELS, SENSITIVITY OF PUSHOVER LOAD TO BENT CAP STIFFNESS, AND EFFECTS OF CONTINUOUS-SPAN SUPERSTRUCTURES 2.1 General A number of ?what if? questions regarding using the Phase II Screening Tool surfaced after submittal of the Phase II Report. Most of these questions pertained to the effect of other loading conditions, scour conditions, height of application of the pushover load, use of continuous superstructures, etc. on the possible pushover failure of a bridge pile bent during an extreme flood/scour event. Answering most of these questions required additional bent pushover analyses, and these are presented and discussed in the sections below. Also, during this interval, ALDOT personnel discovered that there are some sites in Alabama where the estimated maximum scour may be in excess of 20 ft and possibly as large as 25 ft, and thus the pushover analyses needed to be extended to a scour level of 25 ft. Lastly, for completeness, ALDOT personnel wanted to extend the pushover load tables to include 5-pile and 6-pile bents as well as 3-pile and 4-pile bents. The pushover analyses results of these extensions are presented in the following sections. 7 2.2 Sensitivity of Pushover Load to Bent Cap Size/Stiffness Bent caps for all pile bents are either cast-in-place or precast concrete and thus a fair degree of uncertainty occurs about the appropriate value of bending stiffness, I, to use for the cap in a pushover analysis of pile bents. Since many pushover analyses of different bent sizes, bracing conditions, loadings, scour levels, etc., were to be performed, it was decided to conduct a limited sensitivity investigation on the sensitivity of a bent?s pushover load to its cap size/stiffness. Only 3-pile and 4-pile bents of HP10x42 piles that were unbraced, such as the ones shown with qualitative deflection curves in Fig. 2.1, were considered for a rather short and a tall bent height. Values of Igross for the caps of steel pile bents are typically in the range of 25,000 in4 ? Igross ? 50,000. A wide range of I values were used in the analyses, with gross moments of inertia (Igross) ranging from 10,000 in4 to 2,000,000 in4. The I = 2,000,000 in4 value was taken to represent an infinitely stiff cap. The resulting bent pushover loads, Ft, are shown in table form in Table 2.1 and graphically in Fig. 2.2. Fig. 2.1. Qualitative Lateral Load Induced Bent Deformations a. 3-Pile Bent b. 4-Pile Bent 8 Table 2.1. Ft for Unbraced 3-Pile and 4-Pile Bridge Bents for Varying Values of Bent Cap Igross - HP10x42 Piles and P=100k 3-Pile Bent 4-Pile Bent Ft (kips) Ft (kips) Igross (in4) H+S=10? H+S=20? H+S=10? H+S=30? 10,000 25,000 50,000 100,000 150,000 200,000 2,000,000 19.52 19.59 19.61 19.62 19.63 19.63 19.64 4.25 4.30 4.31 4.32 4.33 4.33 4.34 28.40 31.62 34.06 35.92 36.75 37.26 38.61 7.44 11.13 12.47 13.06 13.38 13.49 13.80 Pile Bent Parameters: 9 Fig. 2.2. Pushover Load vs. Bent Cap Igross for Unbraced 3- and 4-Pile Bents (HP10x42 Piles) and P = 100k 10 It can be seen in Table 2.1 and Fig. 2.2 that for the 3-pile bent, the pushover load is essentially independent of the bent cap size/stiffness. For the 4-pile bent the pushover load is sensitive to the cap stiffness at values of Igross ? 100,000 in4. However, even in these cases, the pushover load only decreases by about 19% when I decreases from I = 2,000,000 ? 25,000 in4, which is a 99% decrease in I. These results are consistent with the observation that for steel HP pile bents bending in the plane of the bent, i.e., about the weak axis of the HP piles, the very small value of Ipile relative to the Icap of the concrete cap and the large exposed pile length after scour relative to the length of cap between piles, renders the bending stiffness of the piles to be vastly smaller than that of the cap (see Figs. 2.1 and 2.3). Thus, the flexibility of the bent piles is the controlling bent pushover parameter and the bent pushover load is essentially independent of the cap size/stiffness (within a reasonable range of I values). It is also important to note that the plastic hinges form in the steel HP piles because they have a much smaller plastic moment than that of the bent cap. This also contributes to the pushover failure being independent of the bent cap stiffness. It should be noted that for X-braced bents (see Fig. 2.4) that the bracing system maintains the relative geometrical integrity (with or without the HB-1 brace shown in Fig. 2.4) of the bent in the region of the X-bracing and the bent sidesways in the region below the X-brace as shown in Fig. 2.4. In this case, the pushover load is even more independent of the bent cap Igross. 11 Fig. 2.3. Stiffness and Relative Stiffness Parameters for Typical 3-Pile Bent Fig. 2.4. X-Braced Bent Qualitative Lateral Load-Deformation Behavior 12 2.3 Additional Axial Pile Load Due to Flood Water Loading In checking bent pile plunging or buckling failures we need to give some consideration to the additional pile axial load (?P) caused by flood water loading, Ffw, as shown in Fig. 2.5. We can see from Fig. 2.5 that ?P will be largest for the downstream batter pile for the tallest and narrowest pile bent (3-pile bent). Fig. 2.5. Maximum Pile Load for Checking Pile Plunging and Buckling However we need to determine the magnitude of ?P for other bent sizes to determine whether we need to consider the ?P force in the analyses of those bents. ALDOT Pile Bent Standards indicate the maximum pile bent height above the original ground line (OGL) to be 25 ft. Using this value for bent height, ?H?, a maximum scour of S = 20 ft, a girder/pile spacing (at the bent cap) of 8 ft, and a maximum flood water loading of Ffw = 9.72k, the ?Pmax values of 3-, 4-, 5-pile bents are shown in Fig. 2.6. Thus the additional axial pile load on the downstream bent pile due to the maximum flood water load, Ffw, is fairly 13 insignificant, except for the 3-pile bent. This additional axial load would contribute to trying to ?plunge? or buckle the downstream pile; however, this pile would get some ?lean-on? support from the other piles in the bent. It should be noted that the fwdue to F P = 0?? at a bent and thus the fairly small value of ?Pmax due to the Ffw loading can be and will be neglected. 14 Fig. 2.6. Maximum Additional Axial Pile Load, ?Pmax, Due to Ffw Load 15 2.4 Effect of Continuous-Span Superstructures on Bridge/Bent Pushover The flexural stiffness of a typical bridge deck/curb system bending in a horizontal plane is quite stiff, especially relative to the lateral flexural stiffness of a typical 3-pile or 4-pile bent, as can be seen in Figs. 2.7 and 2.8. Therefore, we can treat the bridge deck as rigid when working with horizontal flood water loadings on a debris raft, i.e., lateral loads in the plane of the deck, and thus all of the deflections due to these loads result from the lateral deflection of the supporting pile bents. For simply-supported 2-span bridges, an accurate modeling for estimating lateral flood water load, Ft, vs deflection behavior of the bridge, and for estimating the load applied to the pile bent would be as shown in Fig. 2.9. For multi-span SS bridges, an accurate modelling would be as shown in Fig. 2.10, and the Ft load would be distributed over all the bents of the bridge. However, most of the Ft load goes to the bents near the Ft load, and a worst case scenario would be to assume the adjacent bents act as abutments in the 2-span bridge of Fig. 2.9. Thus in this case, FB = Ft as it was for the 2-SS span bridge of Fig. 2.9. This is indicated in Fig. 2.10. For a multi-span bridge composed of 2-continuous span segments as shown in Fig. 2.11, we can do the same thing as was done in Fig. 2.10. This is indicated in Fig. 2.11. Bent forces for the simplified modellings shown in Figs. 2.8-2.11 are shown in Fig. 2.12. Note that the resulting bent forces for this approach can be generalized as 16 Applied Bent Max t 1F = F N ? where N = No. of continuous spans in the rigid segments Thus, for a 4-span continuous segment, Applied t Bent Max t F1F = F = 4 4? It should be noted that if the debris raft forms on a bent where the superstructure is continuous, then the Ft force would be applied at this location and the maximum bent force would be half of that occurring when Ft is applied at a bent where the superstructure does not have continuity. This can be seen by comparing the FBent Max forces in Figs. 2.12b and 2.13. Therefore for, SS Bridge: FBent Max Applied = Ft = 12.2k (Includes a F.S. = 1.25 against bent pushover failure) If PushoverCapacityF ? 12.2k the bent is OK for pushover 2-Span Cont: FBent Max Applied = tF2 = 6.1k (Includes a F.S. = 1.25) If PushoverCapacityF ? 6.1k the bent is OK for pushover 3-Span Cont: FBent Max Applied = tF3 = 12.23 = 4.1k (Includes a F.S. = 1.25) If PushoverCapacityF ? 4.1k the bent is OK for pushover 17 4-Span Cont: FBent Max Applied = tF4 = 12.24 = 3.1k (Includes a F.S. (and larger) = 1.25) If PushoverCapacityF ? 3.1k the bent is OK for pushover 5-Span Cont: FBent Max Applied = tF5 = 12.25 = 2.5k (Includes a F.S. (and larger) = 1.25) If PushoverCapacityF ? 2.5k the bent is OK for pushover Fig. 2.7. Lateral Flexural Stiffness of Bridge Deck System vs. Support Pile Bent System 18 a) HP10x42 Unbraced 4-Pile Bent with H=13?, P=120kips and A=6? Pushover Analysis Results b) HP10x42 X-Braced 4-Pile Bent with H=13?, P=120kips and A=6? Pushover Analysis Results Fig. 2.8. Typical Pushover/Lateral Stiffness Curves for Unbraced and X- Braced Pile Bents (from Phase II Report) 19 Fig. 2.9. 2-Span SS Bridge Fig. 2.10. Multi-Span Bridge with Many Rigid SS Spans Fig. 2.11. Multi-Span Bridge Composed of 2-Span Continuous Segments 20 a) SS-Spans or 1-Rigid Span Segments b) 2-Span Continuous Segments c) 3-Span Continuous Segments Fig. 2.12. Maximum Bent Forces for Continuous Span Bridges 21 Fig. 2.13. FBent Max on 2-Span Continuous Bridge when Ft is Applied at Bent Where Superstructure has Continuity 2.5 Effect of Continuous-Span Superstructures on Bent Pile Buckling For continuous superstructures, or those made continuous for LL, a pile or bent cannot buckle in a sidesway mode unless the entire continuous segment does. This would require an unrealistically large loading and thus the piles/bents in continuous spans, or those made continuous for LL, cannot buckle in a sidesway mode. For such continuous superstructure bridges, PCR and Pmax allowed would be as shown in Fig. 2.14 and Table 2.2 for non X-braced bents (see Fig. 2.2 in Phase II Report). Note in Fig. 2.14 that ?max for ALDOT pile bents and maximum anticipated scour levels is 44 ft. Thus, from Table 2.2 if, Pmax applied ? 118k for an HP10x42 pile Pmax applied ? 209k for an HP12x53 pile 22 then the pile/bent will be safe from buckling and doesn?t need to be checked further for buckling. If Pmax applied is larger than the above values, the pile/bent may still be safe depending on the bent height and level of maximum scour at the site. In this case, the bent should be checked for buckling in the manner outlined in the ?screening tool?. Fig. 2.14. Pile Buckling Modes and Equations for Bents Supporting Continuous Bridges 23 Table 2.2. PCR and PMAX ALLOWED for Bent Piles Supporting Continuous-Span Bridge HP10x42 HP12x53 l (ft) PCR (k) P*MAX ALLOWED (k) PCR (k) P*MAX ALLOWED (k) 20 375a 300a 496a 397a 25 330a 264a 460a 368a 30 290a 232a 420a 336a 35 230a 184a 365a 292a 44 147b 118b 261b 209b * Includes a F.S. = 1.25 a Controlled by Pile Inelastic Buckling b Controlled by Pile Elastic Buckling 24 2.6 Pushover Loads for Additional P-load and Scour In the Tier 1 Screening Tool, i.e., the Phase II work, possible pile/bent failures via, 1. pile ?kick-out? 2. pile plunging 3. pile buckling 4. bent pushover were checked for ranges of bent sizes, pile sizes, scour levels, etc. In checking possible pile ?kick-out? failure the criterion used was simply the remaining pile depth of embedment after an extreme flood/scour event. In checking possible pile plunging and pile buckling, PileMax AppliedP was determined for the particular bridge/pile bent and this was compared with the pile PileCapacityP in plunging and Pile CapacityP in buckling. However, in checking possible pile bent pushover, Bent Max AppliedP was determined for the particular bridge/pile bent and this load was assumed to be uniformly distributed to the bent piles as P-loads of Bent Max AppliedP No. of Bent Piles . Using levels of uniformly distributed P-loads (one on the bent cap above each pile) of P = {100, 120, 140, 160k}, pushover analyses were performed on the same range of bent sizes, pile sizes, scour levels, etc. as used in checking the other possible failure modes to determine the lateral pushover capacity, Ft. Thus, tables of bent pushover capacities were determined and these loads could then be compared with the maximum flood water load that could be applied of FMax Applied = 12.2k (includes a F.S. = 1.25) to a bent via hydrodynamic flood water 25 pressure acting on an assumed debris raft developed at the top of the pile bent. For a particular bent, if the pushover capacity, Ft, was greater than the FMax Applied, then the bent was viewed as being safe from pushover failure. It was felt at the time of development of the pushover capacity tables that the P-load range of {100, 120, 140, 160k} would be such that any bent would be subjected to maximum loads in this range. Later, the ALDOT determined that the upper limit of P=160k was adequate for any of their bents, but that the lower limit of P=100k was too large for some of their smaller bridges. They indicated that a P-load level of P=80k should be added to the tables of bent pushover capacities. The ALDOT also noted that only the smaller pile bents had pushover capacities, Ft, low enough to be of concern for a possible pushover failure. Additionally, it was initially felt that a scour level of S=20 ft would be the maximum possible scour at a bridge site in Alabama. However, ALDOT personnel have since found sites where maximum scour levels as high as 22 and 23 ft are estimated. To allow use of the ?ST? at these sites, a maximum scour of 25 ft was added to all of the pushover analyses and tables of pushover capacities. Thus, all pushover capacity tables were expanded to include scour levels of S={0, 5, 10, 15, 20, 25 ft}. About this same time, it was noted that a roadway live load (LL) positioned such that the upstream lane of a bridge was loaded and the downstream lane was not loaded could possibly result in a more severe load condition for pushover capacity than when all lanes were fully loaded (even though the total gravity load on the bent for this load condition would be smaller). This loading 26 condition consisting of an unsymmetric LL distribution is described and discussed more fully in Section 2.7. To address the situations described above, additional pushover analyses with lower uniformly distributed P-loads of P = {60k, 80k} were performed. The P=60k level was added in light of checking the loading case in which LL is not applied to the downstream traffic lane, and also because this loading allowed interpolation of results for uniform P-loads somewhat less than 80k. Initially, in the new pushover analyses conducted for the Phase III work, only the smaller 3-pile and 4-pile bents were analyzed as these were the ones for which it was determined that pushover failure may likely occur in an extreme flood/scour event. However, for completeness, ALDOT desired that pushover results for the 5-pile and 6-pile bents analyses also be included, and this has been done. Results of additional pushover analyses for 3- and 4-pile single-story bents for P-loads of 60k and 80k and scour of 25 ft have been added to those of the earlier analyses for larger P-loads and lower scour levels and these are shown in Tables 2.3-2.6. Also, these tables have been expanded to include 5- and 6-pile bents. One can note in these tables that there is a very dramatic reduction in pushover capacity after 5 ft of scour. For the 3-pile bents, the reduction continues after the first 5 ft of scour but at a reduced rate. For the 4- pile bents, the reduction tends to level out to approximately zero in the scour range of 5 ft < S ? 10 ft, and then the pushover capacity begins to decrease again at a significant rate. The leveling out tends to be more dramatic for the smaller P-load levels. 27 To better illustrate the effect of the P-load level on a bent?s pushover capacity, the data of Tables 2.3-2.6 are shown plotted on Pushover Force vs. H+S curves in Figs. 2.15-2.18. Note in these tables and figures that bents with the lower P-loads of 60k and 80k do have a significantly larger pushover capacity. To better understand the initial drop in pushover capacity, Ft, with scour (or H+S), followed by a leveling off of Ft, and then followed by significant drops in Ft with increases in scour (or H+S) shown in Figs. 2.15 and 2.16, bent Ft vs ? curves contained in earlier reports were revisited and additional GTSTRUDL analyses using different bent end pile batters and cap stiffnesses were performed. Using the Ft vs ? curves shown in Fig. 2.19 taken from Phase II - Part II and plotting the resulting pushover capacity vs H+S curves as shown in Fig. 2.20, bent behavior similar to that reflected in Figs. 2.15 and 2.16 is seen. Using the 5-pile bent, we then investigated its Ft vs S (or H+S) behavior as we varied the batter of the bent end piles and the bending stiffness of the bent cap. The resulting Ft vs S (or H+S) curves for these variations are shown in Fig. 2.21. Note in this figure that when the batter of the end piles is taken away, the pushover force decreased, as expected, as scour is increased, regardless of the stiffness of the bent cap. It can be observed that the behavior without batter is similar to the behavior with batter after the bent reaches a certain plateau point. This point is approximately ten feet of scour for the 5-pile bent of Fig. 2.21. When the stiffness of the bent cap is increased there is a significant increase in pushover force for the first ten feet of scour; however, after ten feet of scour, the increase in pushover force becomes significantly less. It can be concluded that 28 the batter in the end piles causes the stiffness of the bent cap to increase the pushover capacity of the bent, but at a certain scour level, the bent becomes much more flexible and the failure is due to the lack of flexural strength in the piles. It should be noted when the bents are X-braced, they act primarily as vertical trusses when subjected to Ft lateral loads prior to the occurrence of any scour. However, after about 4-5 ft of scour, the smaller flexural stiffness and strength of the piles bending about their weak axis begins to dominate and they act as very flexible bending frames, and thus the dramatic drop in bent pushover force when H+S > 17 ft as indicated in Figs. 2.17 and 2.18. Results of additional pushover analyses for 3, 4, 5, and 6-pile bents that are 2-story and X-braced for P-loads of 60k and 80k and scours of 25 ft have been added to those generated in earlier analyses for larger P-loads and lower scour levels, and these are shown in Tables 2.7 and 2.8. Again, it can be noted in these tables that the lower P-loaded bents have a significantly larger pushover capacity than those with larger P-loads. Lastly, additional pushover analyses for 1-story and 2-story 6-pile bents having double X-bracing across the width of the bent were performed for the additional P-loads of 60k and 80k and for scours of 25 ft, and the results of these analyses are presented in Tables 2.9a and b. All pushover analyses were performed using GTSTRUDL. Example input files for various bent configurations can be viewed in Appendix A. 29 Table 2.3a. Pushover Load, Ft, for Unbraced 3-Pile and 4-Pile Bridge Bents with HP10x42 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4 for Varying Values of P-Load and ?H+S? Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k P=160k 10 0 5 10 15 20 25 10 15 20 25 30 35 21.6 12.9 8.2 4.9 2.0 unstable 20.6 11.5 6.3 2.3 unstable unstable 19.6 10.1 4.3 unstable unstable unstable 20.0 8.9 2.3 unstable unstable unstable 18.8 7.3 unstable unstable unstable unstable 17.6 5.6 unstable unstable unstable unstable 3 13 0 5 10 15 20 25 13 18 23 28 33 38 15.6 9.8 6.1 3.1 unstable unstable 14.4 8.2 3.9 unstable unstable unstable 13.2 6.4 1.5 unstable unstable unstable 12.4 4.7 unstable unstable unstable unstable 11.0 2.8 unstable unstable unstable unstable 9.5 unstable unstable unstable unstable unstable 10 0 5 10 15 20 25 10 15 20 25 30 35 38.3 31.8 30.8 24.8 19.0 13.6 35.7 28.9 27.2 21.6 15.5 10.5 33.5 26.1 24.3 18.2 12.3 7.8 34.8 24.8 22.0 14.8 9.0 5.3 32.3 21.8 18.5 11.6 6.3 3.3 29.9 18.9 15.1 8.4 3.8 1.8 4 13 0 5 10 15 20 25 13 18 23 28 33 38 33.6 30.7 27.8 21.3 15.6 11.0 30.6 27.6 23.8 17.8 12.3 8.3 27.9 24.6 20.8 14.5 9.3 6.0 27.5 22.7 17.8 11.1 6.5 4.0 24.8 19.3 14.3 8.0 4.1 2.5 22.0 16.0 10.9 5.3 2.5 unstable H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 30 Table 2.3b. Pushover Load, Ft, for Unbraced 3-Pile and 4-Pile Bridge Bents with HP12x53 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4 for Varying Values of P-Load and ?H+S? Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k P=160k 10 0 5 10 15 20 25 10 15 20 25 30 35 33.8 21.6 15.4 11.5 8.5 6.1 32.8 20.4 14.0 9.7 6.3 3.2 32.0 19.3 12.5 7.7 3.8 unstable 34.2 18.9 11.2 5.8 1.1 unstable 33.1 17.6 9.6 3.6 unstable unstable 32.0 16.3 7.8 1.4 unstable unstable 3 13 0 5 10 15 20 25 13 18 23 28 33 38 25.3 17.5 12.9 9.6 7.0 4.7 24.3 16.2 11.2 7.5 4.4 unstable 23.3 14.9 9.5 5.3 unstable unstable 23.5 13.9 7.8 2.9 unstable unstable 22.2 12.4 5.9 unstable unstable unstable 21.1 10.9 3.8 unstable unstable unstable 10 0 5 10 15 20 25 10 15 20 25 30 35 56.6 45.4 41.1 40.7 33.3 27.3 53.4 41.6 37.8 37.4 29.6 23.8 50.7 38.8 35.0 33.8 26.6 20.4 54.4 38.7 34.0 31.4 23.4 17.0 52.3 36.2 31.0 28.1 19.9 13.6 50.1 33.7 27.8 24.4 16.5 10.5 4 13 0 5 10 15 20 25 13 18 23 28 33 38 47.3 42.4 41.0 36.7 29.2 23.5 44.3 39.0 37.4 32.6 26.2 20.3 41.7 36.1 35.0 29.0 22.7 16.8 42.8 35.3 33.1 26.9 19.3 13.5 40.5 32.4 29.6 23.1 16.0 10.5 38.1 29.6 26.3 19.5 12.8 7.8 H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 31 Table 2.4a. Pushover Load, Ft, for Unbraced 5-Pile and 6-Pile Bridge Bents with HP10x42 Piles and Reinforced Concrete Cap with Igross = 41,470 in4 of Varying Values of P-Load and ?H+S? Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k P=160k 10 0 5 10 15 20 25 10 15 20 25 30 35 48.1 42.6 44.0 36.5 28.5 21.3 43.8 37.6 38.6 31.9 24.0 17.0 40.6 33.4 34.7 27.0 19.5 13.3 38.2 29.6 29.6 22.6 15.0 9.9 35.8 26.3 24.9 18.1 11.3 6.9 33.4 23.0 20.3 13.9 7.8 4.3 5 13 0 5 10 15 20 25 13 18 23 28 33 38 44.6 41.9 41.3 31.7 24.0 17.6 39.1 37.7 35.6 27.0 19.5 13.9 34.9 32.9 30.8 22.4 15.5 10.5 31.5 28.8 25.6 18.0 11.8 7.5 28.7 24.7 21.2 13.6 8.4 5.0 25.8 20.8 16.8 9.8 5.5 3.0 10 0 5 10 15 20 25 10 15 20 25 30 35 53.1 46.4 47.4 41.0 31.6 24.0 48.2 39.8 41.0 34.7 26.1 19.0 45.2 34.6 35.0 28.2 20.6 14.5 42.7 30.6 28.8 22.4 15.5 10.1 40.0 26.9 23.5 17.0 10.7 6.5 37.3 23.1 17.9 12.0 6.5 4.0 6 13 0 5 10 15 20 25 13 18 23 28 33 38 46.4 45.3 46.0 35.1 27.0 20.3 40.7 38.6 38.1 29.0 21.5 15.5 37.1 33.7 32.4 23.6 16.5 11.5 33.8 28.8 25.7 18.2 12.0 7.8 30.4 24.1 19.7 13.0 8.0 5.0 27.1 19.6 14.3 8.3 4.5 3.0 H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 32 Table 2.4b. Pushover Load, Ft, for Unbraced 5-Pile Bridge Bents with HP12x53 Piles and Reinforced Concrete Cap with Igross = 41,470 in4 for Symmetric Distribution of Varying Values of P-Load and ?H+S? Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k P=160k 10 0 5 10 15 20 25 10 15 20 25 30 35 70.7 60.0 55.6 59.7 49.0 39.9 64.4 52.8 51.5 55.2 43.2 35.3 60.5 49.0 46.3 49.4 39.1 30.9 58.1 44.6 41.8 43.4 34.0 26.3 56.1 41.2 37.7 39.1 29.6 21.8 54.1 38.5 33.9 33.8 25.2 17.5 5 13 0 5 10 15 20 25 13 18 23 28 33 38 60.4 57.2 58.4 53.8 42.7 35.0 55.4 51.7 52.2 48.1 38.5 31.0 51.3 46.7 47.9 42.5 33.8 26.0 47.9 42.5 43.2 38.0 29.4 22.0 45.2 38.4 38.6 32.8 24.9 17.5 42.8 35.0 34.4 28.2 20.5 13.8 10 0 5 10 15 20 25 10 15 20 25 30 35 77.6 61.7 61.2 67.0 55.0 44.3 71.0 56.0 54.3 58.6 48.0 38.4 68.7 51.4 48.2 51.0 41.9 32.9 66.2 47.5 42.9 44.9 35.4 27.6 63.9 44.4 38.2 38.5 29.4 22.3 61.8 41.3 33.9 31.8 23.9 17.2 6 13 0 5 10 15 20 25 13 18 23 28 33 38 66.6 62.4 60.6 60.1 48.1 39.2 60.7 55.6 55.3 52.8 41.9 34.0 55.9 49.1 49.5 46.0 36.0 28.5 52.5 43.8 43.2 39.8 30.5 23.0 49.9 39.5 38.4 33.0 25.0 18.0 47.1 35.9 33.0 26.9 20.0 13.5 H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 33 Table 2.5a. Pushover Load, Ft, for Single Story X-Braced 3-Pile and 4-Pile Bridge Bents with HP10x42 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4 for Symmetric Distribution of Varying Values of P-Load and ?H+S? Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k P=160k 13 0 5 10 15 20 25 13 18 23 28 33 38 46.7 19.1 10.6 5.9 unstable unstable 44.5 17.1 8.5 3.3 unstable unstable 42.5 15.5 6.3 unstable unstable unstable 41.5 14.4 4.0 unstable unstable unstable 39.7 12.8 2.8 unstable unstable unstable 38.3 11.2 unstable unstable unstable unstable 3 17 0 5 10 15 20 25 17 22 27 32 37 42 44.9 17.8 9.6 4.9 unstable unstable 42.9 15.9 7.1 2.0 unstable unstable 41.2 13.9 4.8 unstable unstable unstable 39.9 12.6 2.9 unstable unstable unstable 38.3 10.6 1.0 unstable unstable unstable 36.8 8.7 unstable unstable unstable unstable 13 0 5 10 15 20 25 13 18 23 28 33 38 62.8 35.1 28.7 25.9 19.7 13.3 58.6 31.4 24.6 21.7 15.4 10.0 55.1 28.1 21.0 17.4 11.3 7.0 51.2 24.7 17.3 13.1 8.0 4.1 48.2 22.0 14.0 9.4 5.0 2.0 45.3 19.3 10.9 5.8 1.8 unstable 4 17 0 5 10 15 20 25 17 22 27 32 37 42 58.4 32.7 27.0 23.3 17.0 11.0 53.7 28.7 22.4 18.6 12.4 8.0 49.8 25.1 18.2 14.0 9.0 5.0 45.5 21.4 14.3 9.7 5.0 3.0 42.6 18.3 10.7 5.8 2.1 unstable 40.2 15.5 7.4 2.1 unstable unstable H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 34 Table 2.5b. Pushover Load, Ft, for Single Story X-Braced 3-Pile and 4-Pile Bridge Bents with HP12x53 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4 for Symmetric Distribution of Varying Values of P-Load and ?H+S? Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k P=160k 13 0 5 10 15 20 25 13 18 23 28 33 38 67.7 32.0 19.8 13.5 9.5 6.4 65.9 30.0 17.7 11.3 6.9 unstable 64.0 28.0 15.9 9.1 4.3 unstable 64.8 26.9 14.5 7.5 2.1 unstable 63.1 25.2 12.8 5.3 unstable unstable 61.4 23.8 11.1 3.1 unstable unstable 3 17 0 5 10 15 20 25 17 22 27 32 37 42 66.8 30.6 18.8 12.7 8.6 5.5 64.9 28.4 16.6 10.2 5.8 2.2 62.9 26.5 14.6 7.8 2.9 unstable 61.3 25.1 13.0 5.8 unstable unstable 59.2 23.5 11.1 3.4 unstable unstable 57.2 22.0 9.1 1.1 unstable unstable 13 0 5 10 15 20 25 13 18 23 28 33 38 91.9 53.3 42.5 38.9 35.4 28.2 88.3 49.3 38.4 34.9 30.8 24.1 84.5 45.7 34.8 30.9 26.7 19.9 80.0 41.9 31.0 26.6 22.2 15.6 76.7 38.8 27.8 22.9 18.2 12.0 73.7 35.9 24.7 19.4 14.4 9.0 4 17 0 5 10 15 20 25 17 22 27 32 37 42 85.1 50.9 40.8 37.4 32.5 25.6 82.3 46.4 36.4 32.8 27.9 21.1 79.4 42.4 32.3 28.1 23.3 16.6 76.3 38.2 28.1 23.5 18.7 12.5 72.7 34.9 24.6 19.7 14.6 9.0 69.0 31.8 21.3 15.9 10.7 6.0 H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 35 Table 2.6a. Pushover Load, Ft, for Single Story X-Braced 5-Pile and 6-Pile Bridge Bents with HP10x42 Piles and Reinforced Concrete Cap with Igross = 41,470 in4 for Symmetric Distribution of Varying Values of P-Load and ?H+S? Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k P=160k 13 0 5 10 15 20 25 13 18 23 28 33 38 74.8 44.6 40.0 40.6 31.8 23.0 69.0 39.6 34.2 33.9 26.1 18.0 64.4 35.1 28.9 28.2 20.6 13.6 60.2 31.0 24.0 22.3 15.4 9.6 56.3 27.2 19.5 16.7 10.6 6.0 52.5 23.5 15.3 11.7 6.4 3.5 5 17 0 5 10 15 20 25 17 22 27 32 37 42 69.0 41.7 38.3 37.5 28.8 20.3 63.0 36.0 32.0 30.6 22.8 15.4 57.8 31.2 26.2 24.4 17.1 11.1 53.3 26.9 20.9 18.3 12.0 7.3 49.3 22.8 16.0 12.8 7.4 4.5 45.7 18.9 11.6 7.7 3.6 2.0 13 0 5 10 15 20 25 13 18 23 28 33 38 82.3 49.4 43.9 46.5 36.9 27.4 75.6 43.1 36.8 37.5 29.9 21.3 70.0 37.7 30.2 30.2 23.0 15.8 65.1 32.7 24.4 22.8 16.6 10.6 60.5 28.1 19.0 15.8 10.7 6.3 56.0 23.7 14.0 9.8 5.4 3.0 6 17 0 5 10 15 20 25 17 22 27 32 37 42 76.1 46.0 42.2 43.4 34.0 24.7 68.7 39.3 34.4 34.6 26.6 18.8 62.6 33.5 27.2 26.5 19.8 13.2 57.3 28.4 21.0 18.8 13.3 8.4 52.6 23.6 15.2 12.0 7.5 5.0 48.5 19.1 10.0 6.0 3.0 2.0 H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 36 Table 2.6b. Pushover Load, Ft, for Single Story X-Braced 5-Pile and 6-Pile Bridge Bents with HP12x53 Piles and Reinforced Concrete Cap with Igross = 41,470 in4 for Symmetric Distribution of Varying Values of P-Load and ?H+S? Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k P=160k 13 0 5 10 15 20 25 13 18 23 28 33 38 107.2 66.9 57.5 54.1 55.0 44.0 102.1 61.4 50.9 49.0 48.6 38.5 97.1 56.4 45.2 43.4 42.1 33.0 92.3 52.1 40.6 38.1 36.3 27.5 88.2 47.9 36.2 32.9 30.4 22.3 84.4 44.0 31.8 27.9 24.8 17.3 5 17 0 5 10 15 20 25 17 22 27 32 37 42 99.0 63.4 55.2 54.6 51.8 41.1 95.2 57.5 48.2 47.6 44.7 35.3 91.1 52.4 42.2 41.4 38.1 29.5 84.8 47.6 37.2 35.4 32.0 23.9 80.1 43.2 32.5 29.6 26.0 18.6 76.0 39.1 28.1 24.4 20.3 13.6 13 0 5 10 15 20 25 13 18 23 28 33 38 118.8 74.1 64.1 60.8 63.5 51.7 111.7 67.5 55.4 53.5 54.8 44.4 105.5 61.7 48.6 46.3 46.8 37.4 99.9 56.4 42.8 39.6 39.3 30.6 95.0 51.5 37.5 33.3 31.7 24.1 90.6 46.7 32.3 27.4 24.6 18.0 6 17 0 5 10 15 20 25 17 22 27 32 37 42 108.4 70.1 61.6 59.5 60.8 48.6 103.0 62.7 52.5 51.7 51.8 41.2 96.6 56.6 45.5 43.9 43.2 34.1 90.7 50.9 39.3 36.9 35.5 27.1 85.5 45.7 33.7 29.9 27.6 20.5 80.8 41.0 28.4 23.7 20.4 14.5 H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 37 Fig. 2.15. Pushover Load vs. Bent Height Plus Scour for Unbraced 3- and 4-Pile Bents (HP10x42 Piles) with P-Loads of 60k, 80k, 100k, 120k, 140k, and 160k 38 Fig. 2.16. Pushover Load vs. Bent Height Plus Scour for Unbraced 3- and 4-Pile Bents (HP12x53 Piles) with P-Loads of 60k, 80k, 100k, 120k, 140k, and 160k 39 Fig. 2.17. Pushover Load vs. Bent Height Plus Scour for Single Story X-Braced 3- and 4-Pile Bents (HP10x42 Piles) with P-Loads of 60k and 160k 40 Fig. 2.18. Pushover Load vs. Bent Height Plus Scour for Single Story X-Braced 3- and 4-Pile Bents (HP12x53 Piles) with P-Loads of 60k and 160k 41 a) 3-Pile Bent b) 4-Pile Bent Fig. 2.19a. GTSTRUDL Pushover Analysis Results for 13 ft Tall Non X- Braced HP10x42 Pile Bents Subject to Scour 42 c) 5-Pile Bent d) 6-Pile Bent Fig. 2.19b. GTSTRUDL Pushover Analysis Results for 13 ft Tall Non X- Braced HP10x42 Pile Bents Subject to Scour (cont?d) 43 Fig. 2.20. Pushover Load (Ft) vs. Bent Height Plus Scour (H+S) for 13 ft Tall Unbraced Bents with 6, 5, 4, 3-Piles of HP10x42 and P=100k 44 Fig. 2.21. Pushover Force vs. Scour (H+S) for 5-Pile bent with H=10?, HP10x42 and P=60 kips H + S (ft) 0 10 20 30 40 50 60 70 0 5 10 15 20 25 30 Scour (ft) 1:8 batter / Icap = 41,000 1:8 batter / Icap = inf no batter / Icap = 41,000 or inf 3530252015 4010 45 Table 2.7a. Pushover Load, Ft, for 2- Story X-Braced 3-Pile and 4-Pile Bridge Bents with HP10x42 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4 for Symmetric Distribution of Varying Values of P-Load and ?H+S? Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k P=160k 21 0 5 10 15 20 25 21 26 31 36 41 46 51.3 20.6 11.1 5.8 unstable unstable 48.9 18.4 8.6 2.8 unstable unstable 46.7 16.5 6.1 unstable unstable unstable 44.7 14.5 3.8 unstable unstable unstable 43.2 12.3 unstable unstable unstable unstable 41.3 10.4 unstable unstable unstable unstable 3 25 0 5 10 15 20 25 25 30 35 40 45 50 49.1 19.1 9.9 4.6 unstable unstable 46.9 16.8 7.0 unstable unstable unstable 45.0 14.5 4.3 unstable unstable unstable 43.2 12.1 unstable unstable unstable unstable 41.3 9.8 unstable unstable unstable unstable 39.1 7.6 unstable unstable unstable unstable 21 0 5 10 15 20 25 21 26 31 36 41 46 63.3 32.8 25.0 21.7 16.8 11.3 58.9 28.9 20.6 16.7 12.0 8.0 55.1 25.5 16.8 12.2 7.4 4.1 51.6 22.3 13.2 8.0 4.0 unstable 48.5 19.6 9.7 4.0 unstable unstable 45.6 16.9 6.4 unstable unstable unstable 4 25 0 5 10 15 20 25 25 30 35 40 45 50 58.3 30.1 23.2 19.2 14.4 10.0 53.5 26.1 18.1 14.1 9.4 6.0 49.7 22.3 13.9 9.3 5.0 3.0 46.6 18.9 10.0 4.9 unstable unstable 44.1 15.8 6.4 unstable unstable unstable 41.7 12.8 2.8 unstable unstable unstable H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 46 Table 2.7b. Pushover Load, Ft, for 2- Story X-Braced 3-Pile and 4-Pile Bridge Bents with HP12x53 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4 for Symmetric Distribution of Varying Values of P-Load and ?H+S? Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k P=160k 21 0 5 10 15 20 25 21 26 31 36 41 46 76.0 34.7 21.2 14.2 9.6 6.1 73.8 32.5 18.9 11.6 6.6 2.6 71.6 30.2 16.7 9.1 3.6 unstable 69.4 28.3 14.6 6.5 unstable unstable 67.1 26.6 12.4 4.0 unstable unstable 64.9 24.9 10.2 unstable unstable unstable 3 25 0 5 10 15 20 25 25 30 35 40 45 50 73.4 33.1 19.9 13.1 8.6 5.0 71.4 30.6 17.4 10.3 5.2 unstable 69.3 28.5 15.1 7.4 unstable unstable 67.1 26.5 12.7 4.6 unstable unstable 64.9 24.5 10.2 unstable unstable unstable 62.6 22.5 7.8 unstable unstable unstable 21 0 5 10 15 20 25 21 26 31 36 41 46 95.9 51.6 39.6 35.4 31.3 25.4 92.2 47.5 35.2 30.6 26.2 20.6 88.0 43.8 31.3 25.8 21.4 16.1 84.0 40.3 27.6 21.6 16.8 11.6 80.0 37.0 24.1 17.8 12.6 7.5 76.2 33.9 20.8 14.1 8.6 4.0 4 25 0 5 10 15 20 25 25 30 35 40 45 50 89.6 48.8 37.6 34.0 28.8 23.1 86.4 44.3 32.8 27.9 23.5 18.0 83.1 40.2 28.5 22.7 18.5 13.3 79.7 36.3 24.4 18.5 13.8 8.8 75.8 32.9 20.8 14.4 9.4 5.0 71.7 29.8 17.5 10.5 5.1 unstable H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 47 Table 2.8a. Pushover Load, Ft, for 2-Story X-Braced 5-Pile and 6-Pile Bridge Bents with HP10x42 Piles and Reinforced Concrete Cap with Igross = 41,470 in4 for Symmetric Distribution of Varying Values of P-Load and ?H+S? Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k P=160k 21 0 5 10 15 20 25 21 26 31 36 41 46 75.8 42.4 35.8 35.3 28.8 21.0 69.8 37.3 29.6 28.5 22.5 15.5 64.7 32.8 24.4 21.9 16.5 10.5 60.2 28.6 19.5 15.8 10.9 6.5 56.0 24.6 14.9 10.3 5.7 3.0 52.2 21.0 10.7 5.3 unstable unstable 5 25 0 5 10 15 20 25 25 30 35 40 45 50 69.6 38.4 33.5 32.0 25.5 18.3 63.5 32.8 26.6 24.7 19.1 13.0 58.3 28.0 20.6 17.8 13.0 8.0 53.7 23.5 15.4 11.6 7.3 4.5 49.7 19.5 10.6 6.2 2.8 unstable 46.1 15.8 6.2 unstable unstable unstable 21 0 5 10 15 20 25 21 26 31 36 41 46 84.5 47.8 41.1 40.8 34.8 25.9 76.9 41.3 33.1 32.3 26.5 19.0 70.2 35.5 26.6 24.2 18.9 12.8 64.4 30.5 20.6 16.5 12.0 8.0 59.0 25.8 15.2 9.9 5.6 3.5 54.2 21.3 10.2 4.1 unstable unstable 6 25 0 5 10 15 20 25 25 30 35 40 45 50 76.9 44.3 38.8 38.5 31.7 23.0 69.2 37.3 30.5 29.4 23.4 16.5 62.6 31.4 23.5 20.8 15.8 10.5 57.1 26.2 17.1 13.0 8.8 6.0 52.3 21.4 11.3 6.4 3.1 2.0 48.1 17.2 6.1 unstable unstable unstable H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 48 Table 2.8b. Pushover Load, Ft, for 2-Story X-Braced 5-Pile and 6-Pile Bridge Bents with HP12x53 Piles and Reinforced Concrete Cap with Igross = 41,470 in4 for Symmetric Distribution of Varying Values of P-Load and ?H+S? Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k P=160k 21 0 5 10 15 20 25 21 26 31 36 41 46 114.7 66.3 54.3 51.4 50.3 41.5 108.8 60.3 47.5 44.6 42.8 35.2 102.9 55.0 42.2 38.5 36.5 29.1 97.0 50.2 37.2 32.6 29.7 23.3 91.3 45.7 32.5 27.2 23.4 17.6 86.0 41.5 28.1 22.1 17.6 12.3 5 25 0 5 10 15 20 25 25 30 35 40 45 50 108.9 60.8 51.2 49.4 46.7 38.2 102.5 55.0 43.6 42.0 39.2 31.6 96.3 49.8 37.7 35.1 32.2 25.3 90.3 45.0 32.5 28.6 25.2 19.4 84.8 40.5 27.7 22.6 18.8 13.7 78.6 36.4 23.2 17.5 13.2 8.3 21 0 5 10 15 20 25 21 26 31 36 41 46 128.8 75.0 62.6 59.4 59.2 50.0 120.4 67.6 53.3 50.6 49.5 41.8 112.1 60.8 46.5 42.6 41.4 33.8 104.5 54.7 40.3 35.4 33.0 26.3 96.7 49.0 34.5 28.8 25.0 19.4 90.1 43.9 29.2 22.6 17.8 12.9 6 25 0 5 10 15 20 25 25 30 35 40 45 50 114.3 69.6 59.0 57.4 56.1 46.8 108.2 62.3 50.0 48.1 46.7 38.5 101.9 55.8 42.8 40.0 38.0 30.5 94.2 49.7 36.4 32.0 29.2 23.0 86.3 44.2 30.5 24.9 21.0 16.1 80.4 39.2 25.2 18.6 14.0 9.4 H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 49 Table 2.9a. Pushover Load, Ft, Double X-Braced 1-Story and 2-Story 6-Pile Bridge Bents with HP10x42 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric P-Loads and Scour Pushover Force, Ft (kips) No. Stories and Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k P=160k 13 0 5 10 15 20 25 13 18 23 28 33 38 95.7 50.8 45.4 46.3 37.5 27.3 90.4 44.9 37.9 37.7 30.3 21.2 85.7 39.8 31.4 30.4 23.3 15.8 81.2 34.9 25.7 23.6 17.0 11.0 77.0 30.6 20.6 17.3 11.3 7.0 73.4 26.8 15.9 11.3 6.4 4.0 1- Story and 6-Piles 17 0 5 10 15 20 25 17 22 27 32 37 42 89.3 49.1 44.6 43.5 34.6 24.7 82.5 41.7 35.9 35.3 27.2 18.9 77.8 35.5 28.6 27.6 20.3 13.8 73.9 30.5 22.5 20.5 14.2 9.4 70.5 26.3 17.2 14.0 8.9 6.0 66.6 22.4 12.4 7.9 4.4 3.0 21 0 5 10 15 20 25 21 26 31 36 41 46 98.1 50.6 44.1 43.0 36.7 26.8 92.7 44.6 36.3 34.8 29.0 20.3 88.0 39.4 29.8 27.4 21.8 14.5 83.4 34.5 24.0 20.8 15.2 9.5 79.1 30.4 19.0 14.5 9.3 5.5 75.6 26.7 14.3 8.6 4.1 unstable 2- Story and 6-Piles 25 0 5 10 15 20 25 25 30 35 40 45 50 91.4 48.5 42.8 41.2 33.9 24.0 85.0 41.1 34.1 32.7 26.2 17.9 80.7 35.2 27.0 25.0 18.9 12.5 76.8 30.5 20.9 18.1 12.6 8.0 73.2 26.3 15.8 11.7 7.0 4.1 69.2 22.3 10.9 5.8 2.3 unstable H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 50 Table 2.9b. Pushover Load, Ft, Double X-Braced 1-Story and 2-Story 6-Pile Bridge Bents with HP12x53 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric P-Loads and Scour Pushover Force, Ft (kips) No. Stories and Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k P=160k 13 0 5 10 15 20 25 13 18 23 28 33 38 143.5 76.3 65.3 62.5 63.4 52.1 137.5 69.6 56.4 54.8 54.8 44.8 132.3 64.6 49.6 47.3 46.9 37.7 127.5 59.9 44.1 40.5 39.7 30.8 123.5 55.5 39.0 34.5 32.7 24.4 119.7 51.2 34.2 29.0 26.0 18.4 1- Story and 6-Piles 17 0 5 10 15 20 25 17 22 27 32 37 42 139.3 74.0 64.2 63.4 60.5 49.6 134.0 66.4 55.2 53.7 52.1 41.9 128.4 60.3 47.8 45.3 44.3 34.6 123.3 54.8 41.4 37.9 36.8 27.6 118.5 50.0 35.5 31.5 29.6 21.2 113.6 45.8 30.3 25.7 22.8 15.4 21 0 5 10 15 20 25 21 26 31 36 41 46 149.3 76.9 64.9 62.2 61.3 51.6 143.0 70.8 55.5 53.1 52.1 43.9 137.0 65.7 49.3 45.5 44.3 36.4 131.5 61.0 43.8 38.7 36.6 29.3 126.3 56.5 38.7 32.8 29.5 22.7 121.9 52.1 33.9 27.5 23.0 16.4 2- Story and 6-Piles 25 0 5 10 15 20 25 25 30 35 40 45 50 143.8 74.6 63.8 61.4 58.7 49.1 138.4 67.4 54.6 51.9 50.1 41.0 133.0 61.4 47.3 43.4 42.0 33.5 127.4 55.9 40.8 36.3 34.2 26.3 122.1 51.2 35.2 30.2 27.1 19.7 117.3 47.1 30.4 24.6 20.3 13.7 H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 51 2.7 Pushover Loads for Unsymmetric P-load Distribution The Tier One Screening Tool (T1-ST) assumes a uniform and symmetric P-load distribution across the bent cap as shown in Fig. 2.24. However, this loading may not result in the smallest pushover load, Ft. A smaller but unsymmetrical P-load distribution on the bent resulting from the LL only being applied to the upstream traffic lane as shown in Fig. 2.24 may result in a smaller pushover load. From our earlier Phase II work, pushover failure is only a problem for 3-pile and 4-pile bents. Thus, for these bents, additional pushover analyses were performed for the nonsymmetric P-loading shown in Fig. 2.25. For 3-pile and 4-pile bents, the PDL, PLL, and Ptotal load distributions shown in Figs. 2.22 and 2.23, respectively, were assumed. (See the Phase II Report or Chapter 3 of this report for calculating BentDLP and BentLLP for symmetrical and unsymmetrical loadings). From earlier Phase II work, it was noted that typical span DLs and LLs are such that the unsymmetrical P-loads for 3-pile and 4-pile bents can be taken as shown in Fig. 2.25. These, then, are the distributions and P-load values that were used in the pushover analyses of 3- and 4-pile bents in this Phase III work. 52 Fig. 2.22. 3-Pile Bent P-load Distributions Fig. 2.23. 4-pile Bent P-load Distributions 53 Fig. 2.24. Symmetric and Nonsymmetric P-load Distributions Fig. 2.25. Unsymmetric P-load Levels and Distributions Used in Phase III Work 54 Results of the bent pushover analyses with unsymmetric P-loading, resulting from applying LL only to the bridge upstream lane are presented in Tables 2.10a and 2.10b for single-story, unbraced, 3- and 4-pile bents, and in Tables 2.11a and 2.11b for single-story, X-braced, 3- and 4-pile bents. Again, to better illustrate the effect of P-load distribution on a bent?s pushover capacity, a subset of the data of Tables 2.10a and 2.10b for unbraced bents are shown graphically in Figs. 2.26-2.27, and for braced bents in Figs. 2.28-2.29. As can be seen in all of these figures, the bent pushover load is a little smaller in every case with the unsymmetric P-load distribution. This is due to the sidesway caused by unsymmetric loading. Because the difference is so small, use of pushover analysis having a symmetric P-load distribution was felt to be justifiable. Results of bent pushover analyses with unsymmetric P-loadings on 2- story X-braced 3- and 4-pile bents are presented in Tables 2.12a and 2.12b for HP10x42 and HP12x53 pile bents, respectively. By comparing the pushover loads in Table 2.7a and b with those in Tables 2.12a and b, one can again see that, in every case, the pushover load is a little smaller for the unsymmetric P-load distribution. Again, because of the small difference, restricting pushover analysis to those having a symmetric P-load distribution was felt to be justifiable. Lastly, because of the small difference in pushover results for the unsymmetric P-load distribution relative to that for the symmetric P-load distribution, expansions of the pushover tables were not performed for S = 25ft and for 5-pile and 6-pile bents. 55 Table 2.10a. Pushover Load, Ft, for Unbraced 3-Pile and 4-Pile Bridge Bents with HP10x42 Piles and Concrete Cap with Igross = 41,470 in4 for Unsymmetric P-Loadings and Varying Values of ?H+S? Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k 10 0 5 10 15 20 10 15 20 25 30 19.4 10.8 6.3 3.2 unstable 17.6 8.8 3.9 unstable unstable 16.1 6.8 unstable unstable unstable 14.3 4.7 unstable unstable unstable 12.5 2.4 unstable unstable unstable 3 13 0 5 10 15 20 13 18 23 28 33 13.5 7.9 4.4 unstable unstable 11.6 5.6 unstable unstable unstable 9.8 3.3 unstable unstable unstable 7.8 unstable unstable unstable unstable 5.7 unstable unstable unstable unstable 10 0 5 10 15 20 10 15 20 25 30 36.8 30.5 29.7 23.6 17.5 33.4 26.7 25.5 19.6 13.6 30.4 23.4 21.6 16.1 9.8 27.6 20.1 18.4 12.1 6.0 25.0 17.0 14.5 8.2 2.3 4 13 0 5 10 15 20 13 18 23 28 33 32.5 28.8 26.5 19.8 14.3 28.6 25.5 22.4 16.0 10.3 25.3 22.1 18.3 12.1 6.6 21.9 18.6 14.9 8.3 unstable 19.2 15.1 11.1 4.5 unstable H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 56 Table 2.10b. Pushover Load, Ft, for Unbraced 3-Pile and 4-Pile Bridge Bents with HP12x53 Piles and Concrete Cap with Igross = 41,470 in4 for Unsymmetric P-Loadings and Varying Values of ?H+S? Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k 10 0 5 10 15 20 10 15 20 25 30 31.6 19.5 13.4 9.6 6.8 29.9 17.6 11.3 7.2 4.0 28.3 15.8 9.3 4.8 unstable 26.7 14.0 7.1 2.2 unstable 25.1 12.1 4.8 unstable unstable 3 13 0 5 10 15 20 13 18 23 28 33 23.2 15.5 11.0 7.8 5.4 21.4 13.4 8.7 5.2 2.4 19.7 11.5 6.4 2.6 unstable 18.0 9.5 4.0 unstable unstable 16.2 7.4 unstable unstable unstable 10 0 5 10 15 20 10 15 20 25 30 55.2 43.7 39.5 39.0 32.3 51.3 40.2 36.1 35.4 28.0 48.0 36.3 32.3 31.7 24.1 44.9 33.0 28.9 27.7 20.7 42.3 29.7 25.8 23.5 16.8 4 13 0 5 10 15 20 13 18 23 28 33 45.7 41.1 40.0 35.2 27.9 42.1 37.1 35.6 31.3 24.2 38.9 33.5 31.8 27.0 20.5 35.9 30.2 28.8 23.0 16.5 33.0 26.8 25.1 19.6 12.8 H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 57 Table 2.11a. Pushover Load, Ft, for Single Story X-Braced 3-Pile and 4-Pile Bridge Bents with HP10x42 Piles and Concrete Cap with Igross = 41,470 in4 for Unsymmetric P-Loadings and Varying Values of ?H+S? Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k 13 0 5 10 15 20 13 18 23 28 33 45.1 17.4 8.8 4.3 unstable 42.2 14.6 6.1 unstable unstable 39.7 12.3 3.4 unstable unstable 37.0 10.0 unstable unstable unstable 34.7 7.5 unstable unstable unstable 3 17 0 5 10 15 20 17 22 27 32 37 43.3 16.1 7.9 3.4 unstable 40.6 13.4 4.9 unstable unstable 38.1 11.0 unstable unstable unstable 35.9 8.3 unstable unstable unstable 33.6 5.7 unstable unstable unstable 13 0 5 10 15 20 13 18 23 28 33 61.7 34.0 27.8 25.4 18.7 57.2 29.8 23.3 20.2 14.1 53.1 25.9 19.1 15.9 9.5 49.2 22.2 15.1 11.5 5.0 45.5 18.6 11.2 7.1 unstable 4 17 0 5 10 15 20 17 22 27 32 37 57.8 31.9 26.4 22.5 16.1 52.4 27.4 21.4 17.6 11.1 48.0 23.2 16.7 12.8 6.5 43.9 19.3 12.3 8.0 2.1 40.1 15.5 8.1 3.5 unstable H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 58 Table 2.11b. Pushover Load, Ft, for Single Story X-Braced 3-Pile and 4-Pile Bridge Bents with HP12x53 Piles and Concrete Cap with Igross = 41,470 in4 for Unsymmetric P-Loadings and Varying Values of ?H+S? Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k 13 0 5 10 15 20 13 18 23 28 33 65.5 30.2 18.1 11.8 7.9 62.9 27.6 15.3 9.0 4.8 60.4 25.1 12.8 6.3 unstable 58.0 22.5 10.3 3.5 unstable 55.6 20.2 7.9 unstable unstable 3 17 0 5 10 15 20 17 22 27 32 37 64.5 29.0 17.2 11.1 7.1 61.9 26.2 14.2 8.0 3.8 59.2 23.5 11.6 5.1 unstable 56.4 21.1 9.0 2.0 unstable 53.6 18.8 6.3 unstable unstable 13 0 5 10 15 20 13 18 23 28 33 90.1 52.3 41.8 37.9 34.6 86.0 47.7 37.1 33.5 29.6 81.9 43.6 32.8 29.2 24.8 77.6 39.7 28.7 24.9 20.6 73.6 35.9 24.9 20.6 16.2 4 17 0 5 10 15 20 17 22 27 32 37 83.0 50.1 40.2 37.2 31.8 79.5 45.1 35.2 31.8 26.7 76.0 40.6 30.7 27.0 22.0 72.2 36.4 26.3 22.1 17.3 68.2 32.4 22.1 17.5 12.6 H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 59 Fig. 2.26. Pushover Load vs. Bent Height Plus Scour for Unbraced 3- and 4-Pile Bents (HP10x42 Piles) with Sym. and Unsym. P-Loads 60 Fig. 2.27. Pushover Load vs. Bent Height Plus Scour for Unbraced 3- and 4-Pile Bents (HP12x53 Piles) with Sym. and Unsym. P-Loads 61 Fig. 2.28. Pushover Load vs. Bent Height Plus Scour for Single Story X-Braced 3- and 4-Pile Bents (HP10x42 Piles) with Sym. and Unsym. P-Loads 62 Fig. 2.29. Pushover Load vs. Bent Height Plus Scour for Single Story X-Braced 3- and 4-Pile Bents (HP12x53 Piles) with Sym. and Unsym. P-Loads 63 Table 2.12a. Pushover Load, Ft, for 2-Story X-Braced 3-Pile and 4-Pile Bridge Bents with HP10x42 Piles and Concrete Cap with Igross = 41,470 in4 for Varying Values of ?H+S?and Unsymmetric P-Loadings Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k P=160k 21 0 5 10 15 20 21 26 31 36 41 49.8 19.0 9.4 4.3 unstable 46.7 16.1 6.4 unstable unstable 43.9 13.5 3.4 unstable unstable 41.1 10.9 unstable unstable unstable 38.7 8.2 unstable unstable unstable 36.6 5.6 unstable unstable unstable 3 25 0 5 10 15 20 25 30 35 40 45 47.6 17.5 8.3 3.2 unstable 44.7 14.5 5.0 unstable unstable 42.1 11.8 unstable unstable unstable 39.7 8.8 unstable unstable unstable 37.2 5.8 unstable unstable unstable 34.8 3.0 unstable unstable unstable 21 0 5 10 15 20 21 26 31 36 41 62.3 31.8 24.5 21.3 16.1 57.5 27.5 19.5 15.8 11.1 53.3 23.4 15.1 10.9 6.1 49.2 19.6 10.9 6.2 unstable 45.4 15.9 6.9 unstable unstable 41.9 12.6 3.1 unstable unstable 4 25 0 5 10 15 20 25 30 35 40 45 57.7 29.4 22.9 19.0 13.9 52.3 24.7 17.4 13.3 8.6 47.8 20.6 12.5 8.3 3.4 43.8 16.5 8.0 3.4 unstable 40.2 12.6 3.8 unstable unstable 36.9 9.2 unstable unstable unstable H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 64 Table 2.12b. Pushover Load, Ft, for 2-Story X-Braced 3-Pile and 4-Pile Bridge Bents with HP12x53 Piles and Concrete Cap with Igross = 41,470 in4 for Varying Values of ?H+S?and Unsymmetric P-Loadings Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k P=160k 21 0 5 10 15 20 21 26 31 36 41 73.9 33.0 19.6 12.6 8.1 70.9 30.2 16.5 9.4 4.7 68.1 27.4 13.8 6.4 unstable 65.2 24.7 11.1 3.3 unstable 62.2 22.2 8.4 unstable unstable 59.3 20.0 5.7 unstable unstable 3 25 0 5 10 15 20 25 30 35 40 45 71.2 31.5 18.4 11.6 7.2 68.3 28.4 15.2 8.2 3.4 65.5 25.6 12.3 4.9 unstable 62.6 22.9 9.4 unstable unstable 59.7 20.4 6.4 unstable unstable 56.8 17.9 3.4 unstable unstable 21 0 5 10 15 20 21 26 31 36 41 94.1 50.8 38.9 35.1 30.9 89.9 46.0 34.0 29.7 25.5 85.5 41.9 29.6 24.7 20.3 80.8 37.8 25.3 19.8 15.5 76.2 33.8 21.3 15.3 10.7 71.9 30.2 17.4 11.2 6.2 4 25 0 5 10 15 20 25 30 35 40 45 87.4 48.2 37.2 33.8 28.4 83.5 43.1 31.9 27.7 22.8 79.6 38.6 27.2 22.0 17.6 75.9 34.2 22.6 16.8 12.5 71.5 30.0 18.2 12.2 7.6 67.1 26.2 14.1 7.9 2.9 H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 65 2.8 Pushover Loads for Variable Scour Distribution The Tier One Screening Tool assumes a uniform level of scour along the profile of the bent. However, localized scour at a bridge/pile bent site will not be uniform, but typically will vary from a maximum level at the upstream pile to a minimum level at the downstream pile as shown in Figs. 2.30 and 2.31. Thus, the piles with lower levels of scour can provide some ?lean-on? buckling support and some ?lean-on? plunging support to the piles for which scour is maximum. Also, the piles with lower levels of scour will provide additional pushover load capacity and thus, such bents (with variable scour) will have greater pushover capacity than if all piles in the bent experience Smax. Based on pushover analysis results presented in Phase II Reports (Ramey), only 3-pile bents and a few 4-pile bents appear to be of concern regarding possible pushover failures. Hence, we initially only modeled and analyzed 3-pile and 4-pile bents for pushover loads using a variable scour distribution. In the analyses we assumed the scour distributions shown in Fig. 2.31. An example application problem illustrating the effect of uniform and variable scour on the buckling load for a 3-pile bent is shown in Fig. 2.32. In looking at the results for that problem, the extremely negative effect of scour on bent buckling is obvious. The beneficial effect of a variable scour distribution which allows the piles at the locations of greatest scour to receive significant ?lean-on? support from piles at less severely scoured locations is also obvious. 66 A variable distribution of scour such as that shown in Fig. 2.31 will also result in larger bent plunging failure loads and bent pushover loads, and these will be examined later. 67 Fig. 2.30. Forms of Scour in Rivers: a) Lateral Shift of a Stream Caused by Bank Erosion and Deposition; b) Normal Bottom Scour During Floods; c) Accelerated Scour Caused By a Bridge Pier. [From Sowers, 1962] Fig. 2.31. Assumed Scour Distributions Profile 68 Fig. 2.32. Example Problem Illustrating the Effect of Scour Distribution on Bent Buckling Loads 69 Results of the bent pushover analyses for variable scour distributions for unbraced and X-braced 3, 4, 5, and 6-pile bents are presented in Tables 2.13- 2.16. It can be seen in these tables that when the bent consists of HP12x53 piles, the 4-pile bents are adequate for pushover, and in almost all cases so too are these bents when the piles are HP10x42. However, this is not the case for the 3- pile bents. By comparing the pushover loads in Tables 2.13-2.16 with their ?sister? tables having uniform scour, i.e., Tables 2.3 - 2.6, one can see the significantly larger bent pushover capacity when the scour is not uniform. This is graphically illustrated by plotting a subset of the unbraced and X-braced bent pushover load data vs. H+S in Tables 2.13-2.16, as shown in Figs. 2.33 and 2.34, respectively. Results of bent pushover analyses for variable scour distributions for 2- story X-braced 3, 4, 5 and 6-pile bents with symmetric P-load distribution are shown in Tables 2.17 and 2.18. Comparing the pushover loads in these tables with their ?sister? tables having uniform scour, i.e., Tables 2.7 and 2.8, one can again see a significantly larger pushover capacity when the scour is not uniform. 70 Table 2.13a. Pushover Load, Ft, for Unbraced 3-Pile and 4-Pile Bridge Bents with HP10x42 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4 for Varying Values of P-Load and for Variable Scour and ?H+S? Distributions Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k P=160k 10 0 5 10 15 20 25 10 15 20 25 30 35 21.6 14.8 10.3 7.3 5.1 3.8 20.6 13.4 8.7 5.6 3.7 2.3 19.6 12.0 7.2 4.3 2.3 unstable 20.0 10.7 5.7 3.0 unstable unstable 18.8 9.3 4.5 unstable unstable unstable 17.6 8.0 3.3 unstable unstable unstable 3 13 0 5 10 15 20 25 13 18 23 28 33 38 15.6 11.1 7.8 5.3 3.7 2.5 14.4 9.5 6.0 3.6 2.0 unstable 13.2 7.9 4.3 2.0 unstable unstable 12.4 6.3 2.8 unstable unstable unstable 11.0 4.9 unstable unstable unstable unstable 9.5 3.3 unstable unstable unstable unstable 10 0 5 10 15 20 25 10 15 20 25 30 35 38.3 33.1 31.1 30.3 26.2 23.9 35.7 30.5 27.9 26.9 23.6 21.0 33.5 27.7 25.0 24.1 20.9 17.9 34.8 25.2 22.0 20.0 17.4 15.0 32.3 22.8 19.1 16.9 14.3 12.2 29.9 20.4 16.3 13.8 11.6 9.4 4 13 0 5 10 15 20 25 13 18 23 28 33 38 33.6 31.0 30.3 28.1 24.2 21.2 30.6 28.1 27.3 24.3 21.4 17.8 27.9 25.3 24.3 21.5 18.1 14.6 27.5 22.5 20.8 18.0 14.9 11.5 24.8 19.8 17.6 15.0 11.9 8.5 22.0 17.1 14.5 12.0 8.9 5.8 H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 71 Table 2.13b Pushover Load, Ft, for Unbraced 3-Pile and 4-Pile Bridge Bents with HP12X53 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4 for Varying Values of P-Load and for Variable Scour and ?H+S? Distributions Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k P=160k 10 0 5 10 15 20 25 10 15 20 25 30 35 33.8 24.5 18.5 14.4 11.5 9.2 32.8 23.3 17.0 12.8 9.7 7.3 32.0 22.1 15.6 11.3 8.0 5.9 34.2 20.9 14.3 9.8 6.7 4.8 33.1 19.7 13.0 8.4 5.6 3.5 32.0 18.5 11.7 7.2 4.4 2.3 3 13 0 5 10 15 20 25 13 18 23 28 33 38 25.3 19.4 15.1 11.9 9.5 7.6 24.3 18.0 13.4 10.2 7.6 5.7 23.3 16.7 11.9 8.4 5.9 4.2 23.5 15.3 10.4 6.8 4.5 2.7 22.2 14.0 8.9 5.5 3.1 unstable 21.1 12.7 7.4 4.1 unstable unstable 10 0 5 10 15 20 25 10 15 20 25 30 35 56.6 47.2 43.9 41.5 40.7 38.1 53.4 44.2 40.3 38.2 36.9 34.6 50.7 41.6 37.7 35.0 34.3 30.7 54.4 39.3 34.7 32.1 31.1 27.9 52.3 37.1 31.9 29.0 25.0 24.4 50.1 35.0 29.2 26.0 23.7 20.9 4 13 0 5 10 15 20 25 13 18 23 28 33 38 47.3 42.7 41.5 40.6 38.6 35.1 44.3 40.2 38.2 37.2 33.9 30.8 41.7 37.6 35.2 34.7 31.4 28.2 42.8 34.7 32.5 31.3 28.6 25.0 40.5 32.4 29.5 28.0 25.2 21.9 38.1 30.3 26.6 24.6 21.4 18.9 H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 72 Table 2.14a. Pushover Load, Ft, for Unbraced 5-Pile and 6-Pile Bridge Bents with HP10x42 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric P-Loads and Variable Scour and ?H+S? Distributions Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k P=160k 10 0 5 10 15 20 25 10 15 20 25 30 35 48.1 44.3 42.4 42.6 38.2 32.5 43.8 38.9 37.7 36.2 32.6 28.2 40.6 34.8 32.9 32.1 27.9 23.8 38.2 31.2 28.6 27.2 23.1 19.8 35.8 28.0 24.6 22.5 18.8 16.0 33.4 24.7 20.5 17.9 14.8 12.2 5 13 0 5 10 15 20 25 13 18 23 28 33 38 44.6 42.3 44.4 39.2 33.7 28.3 39.1 37.4 37.8 33.8 29.3 23.9 34.9 33.0 33.4 29.5 24.7 19.6 31.5 28.9 28.7 24.6 20.3 15.3 28.7 25.1 23.9 20.2 16.1 11.5 25.8 21.5 19.5 16.0 12.1 8.1 10 0 5 10 15 20 25 10 15 20 25 30 35 53.1 46.4 46.2 44.3 42.3 38.0 48.2 41.7 39.6 39.0 36.4 32.0 45.2 37.1 34.1 32.8 30.4 26.0 42.7 33.5 29.1 27.0 24.2 20.8 40.0 30.1 24.5 21.5 18.7 15.9 37.3 26.5 20.0 16.2 13.4 11.7 6 13 0 5 10 15 20 25 13 18 23 28 33 38 46.4 45.8 48.5 43.4 38.6 33.3 40.7 39.3 40.0 37.3 33.1 27.3 37.1 34.2 34.0 31.5 27.1 21.8 33.8 29.6 27.9 25.4 21.7 16.8 30.4 25.4 22.7 20.0 16.2 12.3 27.1 21.2 17.6 14.3 11.5 7.9 H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 73 Table 2.14b. Pushover Load, Ft, for Unbraced 5-Pile and 6-Pile Bridge Bents with HP12x53 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric P-Loads and Variable Scour and ?H+S? Distributions Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k P=160k 10 0 5 10 15 20 25 10 15 20 25 30 35 70.7 59.8 56.6 55.9 57.8 52.4 64.4 54.9 52.8 51.9 48.9 46.5 60.5 50.7 47.6 47.1 44.9 41.4 58.1 47.3 43.7 42.1 40.4 36.7 56.1 44.4 39.5 37.4 35.4 31.6 54.1 41.9 36.2 33.0 30.7 26.9 5 13 0 5 10 15 20 25 13 18 23 28 33 38 60.4 58.5 55.9 59.3 53.9 47.7 55.4 53.1 51.7 50.0 47.4 42.6 51.3 47.8 46.6 46.3 42.7 38.3 47.9 43.7 42.4 41.9 38.3 33.3 45.2 39.6 37.6 37.0 33.3 28.7 42.8 36.7 33.7 32.1 28.4 24.7 10 0 5 10 15 20 25 10 15 20 25 30 35 77.6 66.6 60.2 62.0 63.1 58.4 71.0 59.9 55.9 56.0 53.8 50.7 68.7 55.9 51.0 49.2 47.9 45.3 66.2 52.4 46.2 43.5 40.5 39.1 63.9 49.4 42.1 37.9 35.5 33.0 61.8 46.6 38.4 32.9 30.0 27.6 6 13 0 5 10 15 20 25 13 18 23 28 33 38 66.6 59.9 61.7 65.7 59.2 55.4 60.7 55.6 55.4 55.3 51.5 48.3 55.9 50.7 48.9 49.0 46.2 42.7 52.5 45.8 43.8 41.3 40.1 36.4 49.9 42.3 38.6 36.4 34.1 30.2 47.1 39.0 33.9 31.0 28.8 24.9 H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 74 Table 2.15a. Pushover Load, Ft, for Single Story X-Braced 3-Pile and 4-Pile Bridge Bents with HP10x42 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4 for Symmetric Distribution of Varying Values of P-Load and ?H+S? for Variable Scour Distribution Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k P=160k 13 0 5 10 15 20 25 13 18 23 28 33 38 46.7 24.7 15.4 9.9 7.1 5.3 44.5 22.7 13.0 8.3 5.8 3.9 42.5 20.6 11.0 7.1 4.4 2.5 41.5 18.7 9.8 5.7 3.2 unstable 39.7 16.8 8.6 4.5 unstable unstable 38.3 15.0 7.3 3.4 unstable unstable 3 17 0 5 10 15 20 25 17 22 27 32 37 42 44.9 23.1 13.9 9.2 6.7 4.9 42.9 20.8 11.6 7.7 5.1 3.2 41.2 18.6 10.1 6.2 3.6 unstable 39.9 16.5 8.7 4.7 2.1 unstable 38.3 14.6 7.2 3.3 unstable unstable 36.8 13.1 5.8 unstable unstable unstable 13 0 5 10 15 20 25 13 18 23 28 33 38 62.8 40.7 32.1 27.6 24.9 22.0 58.6 37.0 28.1 23.3 20.4 17.8 55.1 33.7 24.5 19.4 16.3 14.1 51.2 30.6 21.1 16.0 12.9 10.7 48.2 27.5 18.1 13.0 9.9 7.9 45.3 24.7 15.2 10.3 7.5 5.5 4 17 0 5 10 15 20 25 17 22 27 32 37 42 58.4 38.5 29.0 25.1 21.8 19.2 53.7 34.7 24.8 20.1 17.1 14.8 49.8 31.3 20.9 16.1 13.1 11.0 45.5 28.2 17.4 12.6 9.7 7.8 42.6 25.1 14.1 9.7 7.1 5.2 40.2 22.3 11.5 7.4 4.8 2.9 H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 75 Table 2.15b. Pushover Load, Ft, for Single Story X-Braced 3-Pile and 4-Pile Bridge Bents with HP12x53 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4 for Varying Values of P-Load and for Variable Scour and ?H+S? Distributions. Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k P=160k 13 0 5 10 15 20 25 13 18 23 28 33 38 67.7 40.9 27.4 19.7 14.6 10.9 65.9 38.9 25.2 17.3 12.2 9.4 64.0 36.8 23.0 15.0 10.8 8.2 64.8 34.9 20.9 13.3 9.6 7.0 63.1 32.9 18.9 12.2 8.5 5.7 61.4 30.8 17.2 11.1 7.2 4.5 3 17 0 5 10 15 20 25 17 22 27 32 37 42 66.8 38.6 26.1 18.6 13.4 10.5 64.9 36.1 23.6 15.8 11.5 9.0 62.9 34.1 21.1 13.8 10.2 7.6 61.3 32.1 18.8 12.6 8.9 6.2 59.2 30.2 17.0 11.3 7.5 4.8 57.2 28.2 15.7 10.0 6.2 3.5 13 0 5 10 15 20 25 13 18 23 28 33 38 91.9 60.7 49.0 42.4 38.6 35.4 88.3 57.5 45.4 38.2 34.0 31.3 84.5 54.1 41.8 34.2 29.9 26.8 80.0 50.9 38.3 30.6 25.9 22.8 76.7 47.8 35.0 27.1 22.4 19.1 73.7 44.8 31.7 24.0 19.2 16.0 4 17 0 5 10 15 20 25 17 22 27 32 37 42 85.1 57.3 45.9 39.6 36.0 32.7 82.3 53.5 42.1 35.4 30.9 27.5 79.4 49.5 38.0 30.9 26.3 23.0 76.3 45.9 34.4 26.9 22.1 19.0 72.7 42.5 30.8 23.2 18.6 15.6 69.0 39.3 27.3 19.9 15.4 12.4 H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 76 Table 2.16a. Pushover Load, Ft, for Single Story X-Braced 5-Pile and 6-Pile Bridge Bents with HP10x42 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric P-Loads and Variable Scour and ?H+S? Distributions Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k P=160k 13 0 5 10 15 20 25 13 18 23 28 33 38 74.8 49.6 40.7 37.6 35.1 31.7 69.0 45.0 35.3 31.7 29.4 26.3 64.4 40.6 30.4 26.5 23.2 20.6 60.2 36.5 25.8 20.7 17.6 15.6 56.3 32.6 21.5 16.2 13.2 11.4 52.5 28.4 17.4 12.3 9.5 8.0 5 17 0 5 10 15 20 25 17 22 27 32 37 42 69.0 44.5 37.2 34.2 31.1 28.0 63.0 39.3 31.4 27.8 25.3 22.4 57.8 34.7 26.2 22.1 19.3 17.2 53.3 30.6 21.2 16.6 14.3 12.6 49.3 26.7 17.0 12.6 10.1 8.6 45.7 23.0 13.3 9.1 6.9 5.5 13 0 5 10 15 20 25 13 18 23 28 33 38 82.3 56.3 46.7 43.1 40.7 38.0 75.6 50.6 40.1 35.3 32.4 30.6 70.0 45.2 34.1 28.6 25.2 23.3 65.1 40.1 28.6 22.3 18.8 16.9 60.5 35.3 23.2 17.1 13.8 12.0 56.0 30.4 18.6 13.0 9.9 8.0 6 17 0 5 10 15 20 25 17 22 27 32 37 42 76.1 50.7 42.4 39.2 37.8 35.3 68.7 44.5 35.5 31.3 29.2 26.9 62.6 39.0 29.3 24.4 21.7 19.5 57.3 33.8 23.5 18.2 15.4 13.7 52.6 29.1 18.5 13.5 10.7 9.1 48.5 24.9 14.5 9.5 6.8 5.3 H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 77 Table 2.16b. Pushover Load, Ft, for Single Story X-Braced 5-Pile and 6-Pile Bridge Bents with HP12x53 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric P-Loads and Variable Scour and ?H+S? Distributions Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k P=160k 13 0 5 10 15 20 25 13 18 23 28 33 38 107.2 74.4 60.8 54.4 51.3 49.6 102.1 69.0 55.4 48.8 45.9 42.6 97.1 64.5 50.7 43.5 40.2 37.5 92.3 60.5 46.3 38.3 34.6 31.3 88.2 56.5 41.8 33.4 28.9 25.5 84.4 52.5 37.6 28.9 23.8 20.8 5 17 0 5 10 15 20 25 17 22 27 32 37 42 99.0 69.7 56.6 50.4 47.6 44.9 95.2 69.2 51.1 44.6 41.8 38.9 91.1 59.4 45.9 39.1 35.6 33.1 84.8 54.7 41.1 33.8 30.0 27.1 80.1 50.4 36.4 28.6 24.5 21.7 76.0 46.2 31.9 23.9 19.7 17.2 13 0 5 10 15 20 25 13 18 23 28 33 38 118.8 84.1 69.7 62.8 60.1 57.8 111.7 77.6 63.0 55.6 52.3 49.2 105.5 72.5 57.2 48.9 44.1 41.0 99.9 67.7 51.7 42.5 37.5 34.0 95.0 62.9 46.3 36.6 31.0 27.3 90.6 58.3 41.2 31.0 25.4 21.8 6 17 0 5 10 15 20 25 17 22 27 32 37 42 108.4 79.1 64.6 58.4 56.0 52.9 103.0 72.4 57.8 51.2 47.7 45.9 96.6 66.6 51.6 44.2 40.0 37.4 90.7 61.3 45.8 37.7 33.2 30.6 85.5 56.1 40.3 31.7 26.8 23.7 80.8 51.2 35.0 26.3 21.4 18.4 H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 78 Fig. 2.33. Pushover Load vs. Bent Height Plus Scour for Unbraced 3-Pile and 4-Pile Bents (HP10x42 Piles) with Uniform and Variable Scour 79 Fig. 2.34. Pushover Load vs. Bent Height Plus Scour for X-Braced 3-Pile and 4-Pile Bents (HP10x42 Piles) with Uniform and Variable Scour 80 Table 2.17a. Pushover Load, Ft, for 2-Story X-Braced 3-Pile and 4-Pile Bridge Bents with HP10x42 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric P-Loadings and Variable Scour and ?H+S? Distributions Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k P=160k 21 0 5 10 15 20 25 21 26 31 36 41 46 51.3 26.7 16.3 10.4 7.4 5.5 48.9 24.4 13.6 8.7 5.9 3.8 46.7 22.1 11.7 7.3 4.3 2.3 44.7 19.9 10.3 5.7 2.9 unstable 43.2 17.7 8.8 4.4 unstable unstable 41.3 15.9 7.3 3.0 unstable unstable 3 25 0 5 10 15 20 25 25 30 35 40 45 50 49.1 24.6 14.4 9.6 6.8 4.9 46.9 22.0 12.1 7.9 5.0 3.0 45.0 19.6 10.5 6.1 3.3 unstable 43.2 17.1 8.8 4.5 unstable unstable 41.3 15.3 7.1 2.9 unstable unstable 39.1 13.5 5.5 unstable unstable unstable 21 0 5 10 15 20 25 21 26 31 36 41 46 63.3 38.8 29.1 24.1 20.8 18.0 58.9 35.2 25.1 19.3 15.8 13.5 55.1 31.7 21.4 15.6 12.1 9.8 51.6 28.5 18.0 12.3 8.9 6.8 48.5 25.4 15.0 9.6 6.5 4.4 45.6 22.5 12.3 7.4 4.4 2.2 4 25 0 5 10 15 20 25 25 30 35 40 45 50 58.3 35.1 26.0 21.0 17.7 15.3 53.5 31.4 21.8 16.4 13.3 11.1 49.7 27.9 18.0 12.6 9.5 7.4 46.6 24.6 14.4 9.4 6.7 4.8 44.1 21.3 11.5 7.1 4.3 2.3 41.7 18.1 9.3 4.9 2.1 unstable H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 81 Table 2.17b. Pushover Load, Ft, for 2-Story X-Braced 3-Pile and 4-Pile Bridge Bents with HP12x53 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric P-Loadings and Variable Scour and ?H+S? Distributions Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k P=160k 21 0 5 10 15 20 25 21 26 31 36 41 46 76.0 44.5 29.3 20.8 15.1 11.4 73.8 41.9 26.8 18.1 12.8 9.8 71.6 39.5 24.4 15.7 11.3 8.4 69.4 37.1 22.1 14.1 10.0 7.0 67.1 35.0 19.9 12.8 8.6 5.5 64.9 32.7 18.0 11.5 7.2 4.2 3 25 0 5 10 15 20 25 25 30 35 40 45 50 73.4 41.2 27.7 19.3 13.9 10.9 71.4 38.9 24.8 16.3 12.1 9.2 69.3 36.6 22.0 14.5 10.5 7.6 67.1 34.4 19.7 13.1 9.0 6.0 64.9 32.3 17.9 11.6 7.4 4.4 62.6 29.9 16.4 10.1 5.9 2.9 21 0 5 10 15 20 25 21 26 31 36 41 46 95.9 59.6 46.8 39.2 34.9 32.1 92.2 56.1 42.9 35.0 30.4 26.5 88.0 52.8 39.2 30.7 25.3 21.5 84.0 49.3 35.6 26.8 21.3 17.8 80.0 46.0 32.2 23.3 17.9 14.5 76.2 42.9 28.7 20.0 14.9 11.5 4 25 0 5 10 15 20 25 25 30 35 40 45 50 89.6 55.9 43.3 36.1 31.6 28.2 86.4 51.7 39.1 31.5 26.7 23.1 83.1 47.8 35.4 27.4 22.0 18.6 79.7 44.1 31.4 23.2 18.2 14.8 75.8 40.6 27.7 19.5 14.7 11.5 71.7 37.6 24.2 16.5 11.9 9.1 H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 82 Table 2.18a. Pushover Load, Ft, for 2-Story X-Braced 5-Pile and 6-Pile Bridge Bents with HP10x42 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric P-Loads and Variable Scour and ?H+S? Distributions Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k P=160k 21 0 5 10 15 20 25 21 26 31 36 41 46 75.8 48.2 37.5 33.0 30.5 27.8 69.8 43.3 32.0 26.9 23.9 21.3 64.7 38.8 26.9 21.1 17.8 15.5 60.2 34.5 22.3 16.1 13.0 11.1 56.0 30.5 18.2 12.4 9.2 7.3 52.2 26.8 14.8 9.2 6.3 4.5 5 25 0 5 10 15 20 25 25 30 35 40 45 50 69.6 42.3 33.2 28.9 26.2 23.6 63.5 37.0 27.2 22.4 19.4 17.3 58.3 32.4 22.0 16.6 13.8 12.2 53.7 28.4 17.5 12.3 9.6 8.1 49.7 24.4 13.6 9.0 6.5 4.8 46.1 20.6 10.6 6.2 3.7 unstable 21 0 5 10 15 20 25 21 26 31 36 41 46 84.5 55.9 44.2 39.4 37.5 35.4 76.6 49.6 37.5 31.8 28.7 26.6 70.2 43.9 31.2 24.7 21.5 19.3 64.4 38.6 25.5 18.8 15.2 13.1 59.0 33.8 20.4 14.3 10.8 8.6 54.2 28.8 16.5 10.6 7.0 4.8 6 25 0 5 10 15 20 25 25 30 35 40 45 50 76.9 49.2 39.9 35.4 33.2 31.7 69.2 42.9 32.8 27.6 24.9 23.0 62.6 37.2 26.6 20.6 17.6 15.7 57.1 32.2 20.9 15.2 12.1 10.3 52.3 27.6 16.5 10.9 7.8 5.9 48.1 23.3 12.6 7.3 4.2 2.2 H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 83 Table 2.18b. Pushover Load, Ft, for 2-Story X-Braced 5-Pile and 6-Pile Bridge Bents with HP12x53 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric P-Loads and Variable Scour and ?H+S? Distributions Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k P=160k 21 0 5 10 15 20 25 21 26 31 36 41 46 114.7 73.6 59.4 51.6 47.9 44.4 108.8 68.3 53.8 45.6 41.0 38.1 102.9 63.6 48.7 39.8 35.0 31.6 97.0 59.0 43.8 34.5 29.1 25.7 91.3 54.5 39.2 29.5 23.7 20.1 86.0 50.3 34.9 25.0 19.4 16.0 5 25 0 5 10 15 20 25 25 30 35 40 45 50 108.9 68.7 54.1 46.6 43.3 40.2 102.5 63.0 47.9 40.3 36.1 33.2 96.3 57.8 42.7 34.2 29.8 26.6 90.3 53.2 37.8 28.7 23.7 20.6 84.8 48.6 33.2 23.7 18.9 16.1 78.6 44.4 28.8 19.8 15.0 12.1 21 0 5 10 15 20 25 21 26 31 36 41 46 128.8 85.3 69.7 61.1 58.3 54.9 120.4 78.3 62.9 53.6 49.2 46.6 112.1 72.3 56.5 46.3 41.6 37.8 104.5 66.6 50.5 39.6 34.1 30.6 97.6 60.9 44.6 33.5 27.5 23.8 90.1 55.6 39.2 28.3 22.1 18.4 6 25 0 5 10 15 20 25 25 30 35 40 45 50 114.3 79.3 63.7 56.5 53.0 50.3 108.2 72.3 56.8 48.7 44.1 41.4 101.9 65.9 50.1 41.4 36.4 33.4 94.2 60.1 44.0 34.8 29.3 26.0 86.3 54.5 38.2 28.5 23.0 19.7 80.4 49.4 32.8 23.3 18.2 15.0 H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 84 Table 2.19a. Pushover Load, Ft, Double X-Braced 1-Story and 2-Story 6-Pile Bridge Bents with HP10x42 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric P-Loads and Variable Scour and ?H+S? Distributions Pushover Force, Ft (kips) No. Stories & Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k P=160k 13 0 5 10 15 20 25 13 18 23 28 33 38 95.7 58.3 46.7 42.9 40.2 37.6 90.4 52.9 39.9 35.1 32.3 30.5 85.7 48.3 34.4 28.6 25.7 23.9 81.2 43.8 29.9 23.6 20.3 18.2 77.0 39.6 25.8 19.3 15.5 13.3 73.4 35.7 22.0 15.0 11.2 8.9 1- Story and 6-Piles 17 0 5 10 15 20 25 17 22 27 32 37 42 89.3 53.9 42.9 38.9 37.1 35.3 82.5 47.9 36.1 31.4 29.4 28.0 77.8 42.8 30.5 25.3 23.1 21.3 73.9 38.1 25.6 20.2 17.4 15.6 70.5 33.8 21.6 15.8 12.5 10.6 66.6 30.5 18.2 12.0 8.5 6.6 21 0 5 10 15 20 25 21 26 31 36 41 46 98.1 58.6 45.8 41.1 38.8 36.7 92.7 53.4 39.3 33.6 31.2 29.2 88.0 48.7 33.9 27.4 24.5 22.3 83.4 44.2 29.5 22.6 18.9 16.6 79.1 40.0 25.4 18.2 14.1 11.5 75.6 36.1 21.6 14.2 9.9 7.3 2- Story and 6-Piles 25 0 5 10 15 20 25 25 30 35 40 45 50 91.4 54.2 42.1 37.7 35.6 33.9 85.0 48.3 35.7 30.2 28.1 26.7 80.7 43.2 30.1 24.4 21.7 20.0 76.8 38.5 25.4 19.3 16.1 14.2 73.2 34.6 21.6 15.1 11.5 9.2 69.2 31.2 18.1 11.4 7.5 5.2 H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 85 Table 2.19b. Pushover Load, Ft, Double X-Braced 1-Story and 2-Story 6-Pile Bridge Bents with HP12x53 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric P-Loads and Variable Scour and ?H+S? Distributions Pushover Force, Ft (kips) No. Stories & Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k P=160k 13 0 5 10 15 20 25 13 18 23 28 33 38 143.5 89.1 69.9 62.3 59.6 56.6 137.5 83.6 63.3 54.9 51.5 48.6 132.3 78.9 57.8 48.1 43.8 40.9 127.5 74.6 52.9 42.1 37.3 34.4 123.5 70.2 48.5 37.5 32.0 28.6 119.7 66.1 44.3 33.4 27.3 23.8 1- Story and 6-Piles 17 0 5 10 15 20 25 17 22 27 32 37 42 139.3 84.4 66.0 59.0 55.3 52.4 134.0 78.1 58.7 50.9 47.0 44.7 128.4 72.4 53.1 44.0 40.0 37.7 123.3 67.3 48.0 38.4 33.7 31.4 118.5 63.0 43.3 33.8 28.8 25.9 113.6 58.8 39.0 29.5 24.2 20.9 21 0 5 10 15 20 25 21 26 31 36 41 46 149.3 90.0 70.6 61.7 59.2 56.0 143.0 84.9 64.2 54.3 49.9 47.5 137.0 80.3 58.9 47.7 42.9 40.0 131.5 75.9 54.0 42.4 36.5 33.5 126.3 71.4 49.4 37.9 31.5 27.9 121.9 67.3 45.1 33.7 27.1 23.3 2- Story and 6-Piles 25 0 5 10 15 20 25 25 30 35 40 45 50 143.8 86.3 66.3 58.4 54.6 52.2 138.4 79.9 59.7 50.6 46.3 43.9 133.0 74.5 54.2 44.2 39.3 36.7 127.4 69.6 49.1 38.9 33.7 30.6 122.1 65.2 44.2 34.1 28.7 25.3 117.3 60.8 39.7 29.7 23.9 20.4 H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line 86 2.9 Pushover Loads for Unsymmetric P-load and Variable Scour Distributions Earlier pushover analyses indicated somewhat smaller bent pushover force for bents loaded unsymmetrically with LL, i.e., the case for which only the upstream lane of the bridge contained a traffic load. Also, earlier analyses indicated an increased bent capacity/pushover load when subjected to a variable scour distribution (rather than to a uniform scour at a level of Smax). Thus, it was of interest to determine which of these opposite effects (nonuniform P-load and nonuniform scour) would have the larger effect on a bent?s pushover capacity. Pushover analyses of 3-pile and 4-pile bents were performed for a combination of these conditions for a range of P-loads including 60 k, 80 k, 100 k, 120 k, and 140k. The results of these analyses are presented in Tables 2.20a and b for unbraced bents with HP10x42 and HP12x53 piles, respectively, and in Tables 2.21a and b for braced bents with HP10x42 and HP12x53 piles, respectively. These tables indicate that for HP12x53 pile bents, all of the 4-pile bents are adequate for pushover, and almost all of the 3-pile bents are adequate as well. This is not the case for the HP10x42 pile bents. For these bents, almost all of the 4-pile bents are adequate, but most of the 3-pile bents are not adequate for pushover. A subset of the pushover loads of Tables 2.20a and 2.21a (for HP10x42 3-pile bents) are shown in Fig. 2.35 for convenience in comparing the effects of nonuniform P-load and scour distributions versus uniform P-load and scour distributions on bent pushover loads. As can be seen in that figure, for unbraced bents, the effect is 87 minimal; however, for X-braced bents, the nonuniform P-load and scour distributions yield significantly higher bent pushover capacities. Results of pushover analyses for 2-story X-braced 3- and 4-pile bents with HP10x42 and HP12x53 piles for unsymmetric P-loads and variable scour distributions are presented in Tables 2.22a and b respectively. By comparing the pushover loads in Tables 2.22a and b with their ?sister? pushover loads for symmetric P-loads and uniform scour in Tables 2.7 and 2.8 respectively, one can see significantly larger pushover capacities for the nonuniform P-load and scour situation. Thus, if one assumes uniform distributions of P-loads and scour, the analyses results will be conservative. 88 Table 2.20a. Pushover Load, Ft, for Unbraced 3-Pile and 4-Pile Bridge Bents with HP10x42 Piles and Concrete Cap with Igross = 41,470 in4 for Unsymmetric P-Loadings and Variable Scour and ?H+S? Distributions Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k 10 0 5 10 15 20 10 15 20 25 30 NN 12.8 8.4 5.5 3.3 NN 10.7 6.2 3.0 unstable NN 8.7 4.0 unstable unstable NN 6.7 unstable unstable unstable NN 4.6 unstable unstable unstable 3 13 0 5 10 15 20 13 18 23 28 33 13.5 9.1 5.9 3.6 unstable 11.6 6.9 3.4 unstable unstable 9.8 4.7 unstable unstable unstable 7.8 2.4 unstable unstable unstable 5.7 unstable unstable unstable unstable 10 0 5 10 15 20 10 15 20 25 30 NN NN NN 29.5 26.5 NN NN NN 25.4 22.5 NN NN NN 21.6 18.4 NN NN NN 18.4 15.2 NN NN NN 14.5 11.5 4 13 0 5 10 15 20 13 18 23 28 33 NN NN 29.3 26.9 23.2 NN NN 25.3 23.1 19.3 NN NN 22.1 18.8 15.9 NN NN 18.6 15.6 12.2 NN NN 14.7 11.9 8.6 H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line NN = Not needed, bent is adequate for uniform scour 89 Table 2.20b. Pushover Load, Ft, for Unbraced 3-Pile and 4-Pile Bridge Bents with HP12x53 Piles and Concrete Cap with Igross = 41,470 in4 for Unsymmetric P-Loadings and Variable Scour and ?H+S? Distributions Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k 10 0 5 10 15 20 10 15 20 25 30 NN NN 16.6 12.6 9.7 NN NN 14.4 10.3 7.3 NN NN 12.3 8.1 5.0 NN NN 10.3 5.9 2.7 NN NN 8.3 3.7 unstable 3 13 0 5 10 15 20 13 18 23 28 33 NN 17.4 13.2 10.0 7.7 NN 15.3 10.8 7.6 5.2 NN 13.3 8.7 5.3 2.7 NN 11.3 6.5 2.9 unstable NN 9.2 4.2 unstable unstable 10 0 5 10 15 20 10 15 20 25 30 NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN 4 13 0 5 10 15 20 13 18 23 28 33 NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line NN = Not needed, bent is adequate for uniform scour 90 Table 2.21a. Pushover Load, Ft, for Single Story X-Braced 3-Pile and 4-Pile Bridge Bents with HP10x42 Piles and Concrete Cap with Igross = 41,470 in4 for Unsymmetric P-Loadings and for Variable Scour and ?H+S? Distributions Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k 13 0 5 10 15 20 13 18 23 28 33 NN 23.2 14.1 8.6 5.3 NN 20.5 11.2 5.8 3.3 NN 18.0 8.4 3.9 unstable NN 15.4 6.0 2.0 unstable NN 13.0 4.1 unstable unstable 3 17 0 5 10 15 20 17 22 27 32 37 NN 21.6 12.8 7.5 4.9 NN 18.8 9.6 5.2 2.8 NN 16.1 7.1 3.3 unstable NN 13.4 5.1 unstable unstable NN 10.7 3.1 unstable unstable 13 0 5 10 15 20 13 18 23 28 33 NN NN 31.4 27.3 25.0 NN NN 27.3 23.0 20.3 NN NN 23.4 18.6 15.7 NN NN 19.5 14.5 11.5 NN NN 15.8 10.9 7.7 4 17 0 5 10 15 20 17 22 27 32 37 NN NN 28.7 24.9 21.8 NN NN 24.4 20.2 17.3 NN NN 20.1 15.7 12.5 NN NN 16.2 11.4 8.3 NN NN 12.3 7.5 4.5 H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line NN = Not needed, bent is adequate for uniform scour 91 Table 2.21b. Pushover Load, Ft, for Single Story X-Braced 3-Pile and 4-Pile Bridge Bents with HP12x53 Piles and Concrete Cap with Igross = 41,470 in4 for Unsymmetric P-Loadings and for Variable Scour and ?H+S? Distributions Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k 13 0 5 10 15 20 13 18 23 28 33 NN NN 26.0 18.4 13.4 NN NN 23.2 15.4 10.3 NN NN 20.6 12.7 7.8 NN NN 17.9 9.9 5.7 NN NN 15.2 7.7 3.9 3 17 0 5 10 15 20 17 22 27 32 37 NN NN 24.9 17.6 12.4 NN NN 21.8 14.2 9.3 NN NN 18.9 11.1 7.2 NN NN 16.0 8.8 5.2 NN NN 13.2 6.9 3.2 13 0 5 10 15 20 13 18 23 28 33 NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN 4 17 0 5 10 15 20 17 22 27 32 37 NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN NN H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line NN = Not needed, bent is adequate for uniform scour 92 Fig. 2.35. Pushover Load vs. Bent Height Plus Scour for Unbraced and X-Braced 3-Pile Bents (HP10x42 Piles) with Uniform P-Load and Scour and with Unsym. P-Load and Variable Scour 93 Table 2.22a. Pushover Load, Ft, for 2- Story X-Braced 3-Pile and 4-Pile Bridge Bents with HP10X42 Piles and Concrete Cap with Igross = 41,470 in4 for Unsymmetric P-Loadings and for Variable Scour and ?H+S? Distributions Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k P=160k 21 0 5 10 15 20 21 26 31 36 41 NA 25.2 15.1 9.0 5.7 NA 22.4 11.9 6.3 3.5 NA 19.6 9.0 4.3 unstable NA 16.8 6.6 2.2 unstable NA 14.1 4.6 unstable unstable NA 11.4 2.6 unstable unstable 3 25 0 5 10 15 20 25 30 35 40 45 NA 23.3 13.4 8.0 5.2 NA 20.2 10.1 5.6 2.8 NA 17.2 7.7 3.4 unstable NA 14.3 5.4 unstable unstable NA 11.4 3.2 unstable unstable NA 9.0 unstable unstable unstable 21 0 5 10 15 20 21 26 31 36 41 NA 38.0 28.6 24.1 21.1 NA 34.0 24.4 19.2 15.8 NA 30.2 20.4 14.6 11.0 NA 26.5 16.4 10.5 7.2 NA 23.0 12.7 7.0 3.5 NA 19.5 9.2 3.6 unstable 4 25 0 5 10 15 20 25 30 35 40 45 NA 34.6 25.8 21.3 18.1 NA 30.3 21.3 16.2 12.9 NA 26.3 17.0 11.7 8.5 NA 22.6 13.1 7.7 4.4 NA 19.1 9.2 3.9 unstable NA 15.6 5.6 unstable unstable H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line NA = Not applicable, no scour present 94 Table 2.22b. Pushover Load, Ft, for 2- Story X-Braced 3-Pile and 4-Pile Bridge Bents with HP12x53 Piles and Concrete Cap with Igross = 41,470 in4 for Unsymmetric P-Loadings and for Variable Scour and ?H+S? Distributions Pushover Force, Ft (kips) No. Bent Piles H (ft) S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k P=160k 21 0 5 10 15 20 21 26 31 36 41 NA 43.2 28.1 19.7 14.0 NA 40.3 25.0 16.4 10.7 NA 37.3 22.1 13.4 8.3 NA 34.5 19.2 10.6 6.2 NA 31.7 16.4 8.4 4.3 NA 28.8 13.7 6.5 2.4 3 25 0 5 10 15 20 25 30 35 40 45 NA 40.0 26.6 18.4 12.8 NA 36.9 23.3 14.7 9.8 NA 34.2 20.0 11.8 7.6 NA 31.4 16.8 9.5 5.5 NA 28.6 14.0 7.4 3.4 NA 26.1 11.7 5.4 unstable 21 0 5 10 15 20 21 26 31 36 41 NA 58.6 46.1 39.1 34.9 NA 54.6 42.0 34.5 30.1 NA 51.0 38.0 30.1 25.4 NA 47.3 34.1 25.9 20.7 NA 43.6 30.4 21.9 16.4 NA 40.0 26.7 18.1 12.6 4 25 0 5 10 15 20 25 30 35 40 45 NA 55.4 43.1 36.2 32.0 NA 50.8 38.7 31.4 26.9 NA 46.6 34.3 26.9 22.0 NA 42.5 30.2 22.4 17.1 NA 38.6 26.3 18.2 13.0 NA 34.8 22.5 14.3 9.3 H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line NA = Not applicable, no scour present 95 2.10 Bent Pushover Failure in Terms of Critical Scour Level As with the original screening tool (ST), the use of linear interpolation of Ft values between values of Ft determined by GTSTRUDL analysis for bent height values after scour, i.e., (H+S) values, which are 5 ft apart, are quite accurate. Thus, we again performed linear interpolation on the capacitytF vs. S (or H+S) data in Tables 2.3 - 2.9 to generate tables of critical uniform scour, SCR, for different levels of P-loads. These tables can in turn be used to determine SCR for a given bent geometry and level of P-load. As with the original ST, Tables 2.3 - 2.9 were used to interpolate values of SCR corresponding to failuretF = 12.15k for each bent geometry configuration, height, and level of P-load. These values of SCR are presented in Tables 2.23 - 2.24, and include a FS = 1.25 on the pushover load, capacity tF . If the resulting SCR > Smax applied at the site, then the bent is safe from pushover failure. The above procedure was repeated for bents with nonuniform scour using the data in Tables 2.13 - 2.19. The resulting values of Scr for nonuniform scour are presented in Tables 2.25 - 2.26, and again these values include a FS = 1.25 on the pushover load, capacitytF . 96 Table 2.23a. Critical Uniform Scour, SCR, of HP10x42 3, 4, 5, 6-Pile Bents without X-Bracing to Resist Ft max design = 12.15k (includes a FS = 1.25) Critical Uniform Scour, SCR (ft)1,2 No. Piles in Bent Bent Height (ft) P = 60k P = 80k P = 100k P = 120k P = 140k P = 160k 10 5.9 4.6 3.9 3.5 2.9 2.3 3 13 3.0 1.8 0.8 0.2 0 0 10 >25.0 23.4 20.0 17.3 14.6 12.2 4 13 23.8 20.2 17.3 14.2 11.7 8.8 10 >25.0 >25.0 >25.0 22.8 19.3 16.4 5 13 >25.0 >25.0 23.4 19.7 16.4 13.3 10 >25.0 >25.0 >25.0 23.1 18.9 14.9 6 13 >25.0 >25.0 24.4 19.9 15.8 12.1 ______________________________ 1 Includes a FS=1.25 on the Pushover Force, F t. 2 If Smax applied< SCR at the site, the bent is safe from pushover failure. 97 Table 2.23b. Critical Uniform Scour, SCR, of HP12x53 3, 4, 5, 6-Pile Bents without X-Bracing to Resist Ft max design = 12.15k (includes a FS = 1.25) Critical Uniform Scour, SCR (ft)5,6 No. Piles in Bent Bent Height (ft) P = 60k P = 80k P = 100k P = 120k P = 140k P = 160k 10 14.2 12.2 10.4 9.4 8.4 7.4 3 13 11.1 9.1 7.5 6.4 5.2 4.4 10 >25.0 >25.0 >25.0 >25.0 >25.0 23.6 4 13 >25.0 >25.0 >25.0 >25.0 23.5 20.6 10 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 5 13 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 10 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 6 13 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 ______________________________ 5 Includes a FS=1.25 on the Pushover Force, F t. 6 If Smax applied< SCR at the site, the bent is safe from pushover failure. 98 Table 2.24a. Critical Uniform Scour, SCR, of HP10x42 3, 4, 5, 6-Pile Bents with X-Bracing to Resist Ft max design = 12.15k (includes a FS = 1.25) Critical Uniform Scour, SCR (ft)3,4 No. Piles in Bent X-Bracing Configuration No. Stories in Bent Bent Height (ft) P = 60k P = 80k P = 100k P = 120k P = 140k P = 160k 13 9.1 7.9 6.8 6.1 5.3 4.8 1- Story 17 8.4 7.1 6.0 5.2 4.7 4.4 21 8.9 8.1 7.3 6.4 5.5 4.9 3 Single-X per Story 2- Story 25 7.5 6.9 6.4 5.3 4.8 4.4 13 >25.0 23.0 19.3 15.9 12.0 9.3 1- Story 17 24.0 20.3 16.9 12.3 9.0 7.1 21 24.2 19.8 14.9 10.9 8.7 7.2 4 Single-X per Story 2- Story 25 22.6 17.0 11.8 8.7 6.9 5.3 13 >25.0 >25.0 >25.0 22.8 18.6 14.2 1- Story 17 >25.0 >25.0 24.1 19.8 15.4 9.5 21 >25.0 >25.0 23.6 18.4 12.7 9.1 5 Single-X per Story 2- Story 25 >25.0 >25.0 20.9 14.9 9.3 6.9 13 >25.0 >25.0 >25.0 23.7 18.5 12.1 1- Story 17 >25.0 >25.0 >25.0 21.2 14.6 8.8 21 >25.0 >25.0 >25.0 19.7 12.6 9.0 6 Single-X per Story 2- Story 25 >25.0 >25.0 23.4 15.7 9.4 7.0 13 >25.0 >25.0 >25.0 24.0 19.1 13.9 1- Story 17 >25.0 >25.0 >25.0 22.1 16.7 10.1 21 >25.0 >25.0 >25.0 22.7 16.9 11.5 6 Double-X per Story 2- Story 25 >25.0 >25.0 >25.0 20.3 14.0 9.3 _________________________ 3 Includes a FS=1.25 on the Pushover Force, F t. 4 If Smax applied < SCR at the site, the bent is safe from pushover failure. 99 Table 2.24b. Critical Uniform Scour, SCR, of HP12x53 3, 4, 5, 6-Pile Bents with X-Bracing to Resist Ft max design = 12.15k (includes a FS = 1.25) Critical Uniform Scour, SCR (ft)7,8 No. Piles in Bent X-Bracing Configuration No. Stories in Bent Bent Height (ft) P = 60k P = 80k P = 100k P = 120k P = 140k P = 160k 13 16.7 14.3 12.8 11.7 10.4 9.6 1- Story 17 15.7 13.5 11.8 10.6 9.6 8.8 21 15.5 14.3 13.2 11.8 10.5 9.6 3 Single-X per Story 2- Story 25 14.3 13.2 12.2 10.7 9.6 8.8 13 >25.0 >25.0 >25.0 >25.0 24.9 22.0 1- Story 17 >25.0 >25.0 >25.0 >25.0 22.2 18.6 21 >25.0 >25.0 >25.0 24.5 20.4 16.6 4 Single-X per Story 2- Story 25 >25.0 >25.0 >25.0 21.7 17.1 13.7 13 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 1- Story 17 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 21 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 5 Single-X per Story 2- Story 25 >25.0 >25.0 >25.0 >25.0 >25.0 21.1 13 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 1- Story 17 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 21 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 6 Single-X per Story 2- Story 25 >25.0 >25.0 >25.0 >25.0 >25.0 22.0 13 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 1- Story 17 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 21 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 6 Double-X per Story 2- Story 25 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 _________________________ 7 Includes a FS=1.25 on the Pushover Force, F t. 8 If Smax applied < SCR at the site, the bent is safe from pushover failure. 100 Table 2.25a. Critical Nonuniform Scour, SCR, of HP10x42 3, 4, 5, 6-Pile Bents without X-Bracing to Resist Ft max design = 12.15k (includes a FS = 1.25) Critical Nonuniform Scour, SCR (ft)1,2 No. Piles in Bent Bent Height (ft) P = 60k P = 80k P = 100k P = 120k P = 140k P = 160k 10 7.9 6.3 4.9 4.2 3.5 2.8 3 13 3.8 2.3 1.0 0 0 0 10 >25.0 >25.0 >25.0 >25.0 >25.0 18.8 4 13 >25.0 >25.0 >25.0 >25.0 24.0 19.6 10 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 5 13 >25.0 >25.0 >25.0 >25.0 24.3 19.9 10 >25.0 >25.0 >25.0 >25.0 >25.0 23.7 6 13 >25.0 >25.0 >25.0 >25.0 >25.0 18.8 ____________________________ 1 Includes a FS=1.25 on the Pushover Force, F t. 2 If Smax applied< SCR at the site, the bent is safe from pushover failure. 101 Table 2.25b. Critical Nonuniform Scour, SCR, of HP12x53 3, 4, 5, 6-Pile Bents without X-Bracing to Resist Ft max design = 12.15k (includes a FS = 1.25) Critical Nonuniform Scour, SCR (ft)5,6 No. Piles in Bent Bent Height (ft) P = 60k P = 80k P = 100k P = 120k P = 140k P = 160k 10 18.9 16.0 14.0 12.4 10.9 9.7 3 13 14.6 12.0 9.7 8.2 6.8 5.5 10 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 4 13 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 10 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 5 13 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 10 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 6 13 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 ______________________________ 5 Includes a FS=1.25 on the Pushover Force, F t. 6 If Smax applied< SCR at the site, the bent is safe from pushover failure. 102 Table 2.26a. Critical Nonuniform Scour, SCR, of HP10x42 3, 4, 5, 6-Pile Bents with X-Bracing to Resist Ft max design = 12.15k (includes a FS = 1.25) Critical Nonuniform Scour, SCR (ft)3,4 No. Piles in Bent X-Bracing Configuration No. Stories in Bent Bent Height (ft) P = 60k P = 80k P = 100k P = 120k P = 140k P = 160k 13 13.0 10.9 9.4 8.7 7.8 6.9 1- Story 17 11.9 9.7 8.8 7.8 6.7 5.7 21 13.5 11.5 9.8 9.0 8.1 7.2 3 Single-X per Story 2- Story 25 12.3 10.0 9.1 8.0 6.9 5.8 13 >25.0 >25.0 >25.0 21.7 16.4 13.1 1- Story 17 >25.0 >25.0 22.3 15.8 12.2 9.7 21 >25.0 >25.0 19.9 15.2 12.6 10.2 4 Single-X per Story 2- Story 25 >25.0 22.6 15.7 12.3 9.7 8.4 13 >25.0 >25.0 >25.0 >25.0 22.9 15.3 1- Story 17 >25.0 >25.0 >25.0 >25.0 15.9 11.4 21 >25.0 >25.0 >25.0 22.2 15.4 12.4 5 Single-X per Story 2- Story 25 >25.0 >25.0 >25.0 15.3 11.6 9.2 13 >25.0 >25.0 >25.0 >25.0 24.6 16.4 1- Story 17 >25.0 >25.0 >25.0 >25.0 17.4 12.4 21 >25.0 >25.0 >25.0 >25.0 18.1 13.7 6 Single-X per Story 2- Story 25 >25.0 >25.0 >25.0 19.9 13.9 10.4 13 >25.0 >25.0 >25.0 >25.0 >25.0 18.9 1- Story 17 >25.0 >25.0 >25.0 >25.0 20.9 14.9 21 >25.0 >25.0 >25.0 >25.0 23.8 17.4 6 Double-X per Story 2- Story 25 >25.0 >25.0 >25.0 >25.0 19.1 14.4 _________________________ 3 Includes a FS=1.25 on the Pushover Force, F t. 4 If Smax applied < SCR at the site, the bent is safe from pushover failure. 103 Table 2.26b. Critical Nonuniform Scour, SCR, of HP12x53 3, 4, 5, 6-Pile Bents with X-Bracing to Resist Ft max design = 12.15k (includes a FS = 1.25) Critical Nonuniform Scour, SCR (ft)7,8 No. Piles in Bent X-Bracing Configuration No. Stories in Bent Bent Height (ft) P = 60k P = 80k P = 100k P = 120k P = 140k P = 160k 13 23.3 20.1 18.4 16.6 15.1 14.1 1- Story 17 22.2 19.2 17.3 15.6 14.3 13.1 21 24.0 21.0 19.0 17.4 15.8 14.5 3 Single-X per Story 2- Story 25 22.9 19.9 17.9 16.2 14.6 13.4 13 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 1- Story 17 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 21 >25.0 >25.0 >25.0 >25.0 >25.0 24.0 4 Single-X per Story 2- Story 25 >25.0 >25.0 >25.0 >25.0 24.0 19.7 13 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 1- Story 17 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 21 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 5 Single-X per Story 2- Story 25 >25.0 >25.0 >25.0 >25.0 >25.0 24.9 13 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 1- Story 17 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 21 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 6 Single-X per Story 2- Story 25 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 13 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 1- Story 17 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 21 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 6 Double-X per Story 2- Story 25 >25.0 >25.0 >25.0 >25.0 >25.0 >25.0 _________________________ 7 Includes a FS=1.25 on the Pushover Force, F t. 8 If Smax applied < SCR at the site, the bent is safe from pushover failure. 104 2.11 Check Upstream Bent Pile for Beam-Column Failure from Debris Raft Loading In extreme flood/scour events, a debris raft and flood water loadings, Ft, on this raft may occur at a bridge support bent. The raft and loading may be applied to a pile bent as high as the bottom of the bent cap, and this would be the critical location in checking for bent pushover adequacy. This is where the loading was applied in all of the pushover analyses in the Phase II work. (See the HWL1 and Ft1 positions in Fig. 2.36.) However, the Ft loading could also be applied at a lower position on the bent and this would be the critical location in checking the upstream pile for failure as a beam-column. (See HWL2 and Ft2 positions in Fig. 2.36.) Before checking the upstream pile for adequacy as a beam-column, consider it as a vertical beam with pinned-ends, as shown in Fig. 2.37. Note in Fig. 2.37 that the debris raft loading, Ft2, which will henceforth be denoted as Ft, is assumed to be applied 7.5 ft down from the top of the pile and the distance from Ft to the new river bottom varies as shown. depending on the level of scour, S. This height was determined by acknowledging that the tallest unbraced bent is 13 ft. The worst case scenario for maximum applied moment due to Ft was found to be at a height of 7.5 ft from the top of the pile. Using Mmax in Fig. 2.37, which occurs at the location of the Ft loading for the maximum scour, i.e., (H+S)max condition, and assuming the pile is an HP10x42, then for a maximum height unbraced bent, 105 '"/'k max max 3 M 57.74 12 = = = 48.8 ksi (for S=25 ft) S 14.2 in? ? 3 "k 'kP y yM = Z = 21.8 in 36 ksi = 785 65.4?? ? = Thus an HP10x42 pile would have significant local yielding at the Mmax location, but it would be adequate for the beam-only loading. If the pile is an HP12x53, then '"/'k max 3 57.74 12 = = 32.8 ksi (for S=25 ft) 21.1 in? ? 3 "k 'k P y yM = Z = 32.2 in 36 ksi = 1159 96.6?? ? = the pile would be adequate and would not experience any local yielding. If a fixed-end condition is assumed for the pile, the resulting Mmax and ? max for an HP10x42 pile would be as shown in Fig. 2.38. For these end conditions, the pile would be adequate but would have some small local yielding at the Mmax location. Actual end conditions for the bent pile would be somewhere between pinned and fixed, but probably closer to fixed. For bents with X-bracing, which all taller bents should have, the horizontal strut, or bracing member, will serve to distribute the Ft force to all piles in the bent (see Fig. 2.39). Therefore these bents will be adequate for the lower Ft loading position. If there is no horizontal strut, the diagonal L 4?x3??x5/16? brace will be sufficiently strong in compression to prevent the upstream pile from failing in bending (see Fig. 2.39). 106 Fig. 2.36. Maximum Height Unbraced Bent Showing Two HWL and Ft Locations Fig. 2.37. Upstream Pile, P1, Mmax Values for Pinned-End Condition 107 Fig. 2.38. Upstream Pile, P1, Mmax Values for Fixed-End Condition 108 Fig. 2.39. X-Braced Bent with Ft-Load at Level of Horizontal Brace 109 The analyses above neglected the axial P-load on the upstream pile. We now need to consider this load and analyze the pile as a beam-column. To do this we will use the approximate straight-line interaction equation u u P M + 1.0 P M ? (2.1a) or, cr P P M + 1.0 P M ? (2.1b) to determine its adequacy. For our maximum height unbraced bent shown in Fig. 2.36 with P=100k and the HWL and Ft being at level 2 as shown in Fig. 2.40, and assuming the bent has full fixity at both ends, HP10x42 piles, and cannot buckle in a sidesway mode, a check of the adequacy of the upstream pile as a beam-column is as shown in Fig. 2.40. It should be noted that only the bent?s upstream pile is acting primarily as a beam-column with a significant value of M/Mp. Thus, the other piles in the bent will provide lean-on buckling support for the upstream pile, i.e., for a sidesway buckling mode to occur all of the piles in the bent must be loaded to their sidesway buckling capacity. This will not be the case and thus the bent and the upstream pile will not sidesway. Note in Fig. 2.40 that the upstream pile would not be adequate for the low level position of the Ft load if the scour is extremely large, i.e., S > 20ft if the bent piles are HP10x42. However, if the piles are HP12x53 or larger, the upstream pile is adequate for S ? 25 ft. 110 Fig. 2.40. Checking Upstream Pile of Maximum Height Unbraced Bent as a Beam-Column 111 As can be seen in Figs. 2.38 and 2.40 for unbraced bents, the larger the bent height, H, and scour, S, the longer the unsupported length, ?, of the upstream pile, and this means the smaller the pile buckling load, Pcr, and the larger the applied moment, M, leading to a larger value on the lefthand side of the interaction equation, Equation 2.1. Also, as indicated in Fig. 2.40, the relationship of the upstream pile unsupported length and the bent height and level of scour is ? = H + S - 2? (2.2) Thus, for a maximum height unbraced bent of H=13 ft, Eqn 2.2 can be used to determine the unsupported length of the upstream pile for different levels of scour, Mmax applied can be determined from the equation in Fig. 2.38 and Pcr can be determined from the equation in Fig. 2.40. With these values and a knowledge of Mp for the various HP piles, Eqn 2.1 can be used to determine the applied P-load level necessary for the left side of Eqn 2.1 to equal unity, thus indicating incipient failure, as indicated below. For H=13? and S=20? ? = H + S - 2? = 13+20-2 = 31? 22 2 / 4 2 2 I 29,000 71.7 31 144 y k cr 2 2 E 2P = = = 297k in in in pi pi ? ? ?l Mmax = 41.9?k (see Fig. 2.38) ' 3 k p y "/ 36ksi 21.8in M = Z = = 65.4' 12? ?? k k k k cr p P M P 41.9 41.9 = 1.0 = 1 P= 1- 297 P M 297 65.4 65.4 ? ?? + ? + ? ? ? ? ? P=0.359 x 297k =107k 112 ?For the maximum height unbraced bent with HP10x42 piles and a maximum scour level of Smax=20 ft, if Papplied < 107k the upstream pile is safe Papplied ? 107k the upstream is not safe The procedure above was employed for different levels of scour, and the resulting appliedfailureP loads are shown in Table 2.27. It should be noted in Table 2.27. that for S=0, 5ft, and 10ft, axial yielding of the pile (rather than buckling) controls and Py was used in Eqn 2.1. Also, for S=15ft and 20ft, the Pcr values shown in Table 2.27 are for elastic buckling and adjusted values are also shown and recommended since inelastic buckling would occur for these levels of scour. An interaction diagram of axial Pfailure vs Scour using the data in Table 2.27 is shown in Fig. 2.41. Both the unadjusted and adjusted (for inelastic buckling) failure curves are shown on the figure as well as safe and unsafe combinations of applied pile axial load P and scour S. Table 2.27 Upstream Pile Beam-Column Failure for Lower Elevation Debris Raft with Ft=9.72k and H=13 ft Unbraced Bent with HP10x42 Piles H (ft) S (ft) ? (ft) applied maxM (ft-kips) Mp (ft-kips) Pbuckle (kips) Pyield (kips) Pcr (kips) Pfailure (kips) 13 13 13 13 13 13 0 5 10 15 20 25 11 16 21 26 31 36 15.8 20.6 30.1 36.9 41.9 45.7 65.4 65.4 65.4 65.4 65.4 65.4 2355 1113 646 422 297 220 446 446 446 446 446 446 446 446 446 422* 297* 220 338 306 241 160 100 66 *Somewhat high as they assume elastic buckling whereas inelastic buckling would occur at these scour levels 113 Fig. 2.41 Interaction Diagram of Axial Pfailure vs. S for the Upstream Pile for Unbraced Bents with H=13 ft and HP10x42 Piles 114 Two-story bents will always be X-braced with the bottom of the lower X- brace being located 3?-6? above the original ground line. Thus, if extreme scour of such a bent were to occur during high-water flood conditions, the HWL and flood debris raft would be located somewhere in the X-braced region of the bent. In this case, the upstream bent pile would not be subjected to significant bending/beam-column forces and stresses and need not be checked for a beam- column failure. Such bents should be checked for possible pushover failure, and the effect of height of HWL and debris raft location on such bents is discussed in Section 2.12. In summary, for X-braced bents, both single-story X-braced and two-story X-braced, the upstream bent pile is adequate as a beam-column for debris raft lateral loading, Ft, at any elevation along the pile. For unbraced bents, the taller the bent, the more likely the upstream pile might not be adequate as a beam- column for a debris raft forming at a lower elevation below the bent cap. If the unbraced bent has HP12x53 or larger piles, then the upstream pile is adequate as a beam-column no matter where the debris raft forms. However, if the unbraced bent has HP10x42 piles, then the tallest such bent (prior to scour) should be one with H=13 ft, and for such a bent, the interaction diagram of Fig. 2.41 indicates the following for the upstream pile: P=160k ? Sfailure = 15? ? Ssafe = 12? P=140k ? Sfailure = 16.6? ? Ssafe = 13.3? P=120k ? Sfailure = 18.3? ? Ssafe = 14.6? P=100k ? Sfailure = 20? ? Ssafe = 16? P=80k ? Sfailure = 23? ? Ssafe = 18.4? P=60k ? Sfailure = 27? ? Ssafe = 21.6? 115 Thus, only unbraced pile bents need to be checked for adequacy of the upstream pile as a beam-column, and for these bents, only those with HP10x42 or smaller piles need to be checked. Also, only those unbraced bents with HP10x42 or smaller piles that have a height, H, and high water level, HWL, such that a debris raft could likely form at the lower elevation level need to be checked. The adequacy of the bent upstream pile as a beam-column, summarized above, are further summarized in more concise flowchart form in Fig. 2.42. 116 Is the bent X-braced? Fig. 2.42 Checking Adequacy of Bent Upstream Pile as a Beam-Column Are the bent piles larger than HP10x42? Upstream pile is OK as a beam-column! No Yes Is there a source or history of flood debris such that a debris raft could form? Upstream pile is OK as a beam-column! Upstream pile is OK as a beam-column! Are the bent height, H, and high water level, HWL, such that during an extreme flood event a debris raft could likely form 7 ft or more below the top of the bent cap? Upstream pile is OK as a beam-column! Then for P = 160k? Sfailure = 15? and safemaxS = 12? P = 140k? Sfailure = 16.6? and safemaxS = 13.3? P = 120k? Sfailure = 18.3? and safemaxS = 14.6? P = 100k? Sfailure = 20? and safemaxS = 16? P = 80k? Sfailure = 23? and safemaxS = 18.4? P = 60k? Sfailure = 27? and safemaxS = 21.6? at the site, and at the site is, Smax > safemaxS ? Upstream pile is OK as a beam- column! Bent upstream pile should be checked more closely for possible failure as a beam-column No No No No Yes Yes Yes Yes 117 2.12 Effect of Height of Debris Raft Loading on Bent Pushover In extreme flood/scour events, a debris raft may develop at a pile bent, and the resulting dominant flood water loading, Ft, on the bent may occur as high on the bent as the bottom of the pile cap and this was the position of Ft assumed in the Phase II work. However, the topology at some bridge locations may be such that tall bents are required to achieve an appropriate roadway elevation, but the high water level at the site may be significantly lower than the top of the bent cap. It was anticipated that this would be a less severe bent pushover load condition relative to that of the load located at the bottom of the bent cap, as was used in the Phase II work. GTSTRUDL pushover analyses were performed for the family of relatively tall two-story X-braced 3- and 4-pile bents of HP10x42 piles shown in Fig. 2.43. Each bent had a height, ?H? of 21 ft and was subjected to P- loads of {P} = {60, 80, 100, 120, 140k, 160k} and scour levels of {S} = {0, 5?, 10?, 15?, 20?, 25?} and had the pushover force, Ft, applied at 2?-0 below the top of the cap, i.e., at the bottom of the bent cap, and at 9?-6? below the top of the cap, i.e., at the location of the bent horizontal strut, as shown in Fig. 2.43. The resulting pushover forces for the bents are shown in Table 2.28, and as evident from that table, the higher location of the Ft load did not prove to be the most severe load location. Rather, the lower location of Ft yielded pushover loads approximately 8% - 12% lower than the high location of Ft. Essentially, the analyses results indicate that the vertical position of the flood water horizontal loading, Ft, doesn?t significantly affect the bent pushover load, as the bent bracing system is effective in maintaining the relative 118 geometrical relationships of the bent members in the region of X-bracing. Thus, almost all of the bending deformations of the bent occur in the lower unbraced region, and are essentially independent of where Ft is applied in the upper braced region, as shown in Fig. 2.44. This weak axis pile bending in the lower unbraced region is the primary cause of the lateral deflections at the top of the bent, and is the cause of the bent pushover failures. GTSTRUDL-generated deformation curves for 3- and 4-pile bents with the Ft loading located at the bottom of the bent cap and at the location of the horizontal strut are shown in Figs. 2.45 and 2.46. An additional family of pushover analyses were conducted on an X- braced, 2-story, 3-pile bent with the lateral load applied at the level of the bent horizontal brace for the P-load and scour levels indicated in the figure at the bottom of Table 2.29. Five different combinations of axial and flexural stiffnesses of the horizontal brace were used in the analyses to gain an understanding of the importance of the horizontal brace stiffness on the bent pushover load. The results of these analyses are summarized in Table 2.29, and indicate that the bent pushover load is also essentially independent of the stiffness of the bent horizontal brace. 119 Fig. 2.43. Two-Story X-Braced 3-Pile Bent with Horizontal Flood Water Load, Ft, Applied at Bottom of Cap or Location of Horizontal Strut in GTSTRUDL Pushover Analyses 120 Table 2.28. Pushover Load, Ft, at High or Low Position for 2-Story X-Braced 3-Pile and 4-Pile Bridge Bents of Height H=21 ft with HP10x42 Piles and Concrete Bent Cap with Igross = 41,470 in4 for Symmetric P-Loads and Uniform Scour Pushover Force, Ft (kips) No. Bent Piles Ft Position S (ft) H+S (ft) P=60k P=80k P=100k P=120k P=140k High (Bottom of Cap) 0 5 10 15 20 21 26 31 36 41 45.1 20.6 11.1 5.8 UNS 48.9 18.4 8.6 2.8 UNS 46.7 16.5 6.1 UNS UNS 44.7 14.5 3.8 UNS UNS 43.2 12.3 UNS UNS UNS 3 Low (Horiz. Strut) 0 5 10 15 20 21 26 31 36 41 45.1 18.2 9.8 5.1 UNS 43.0 16.3 7.6 2.5 UNS 40.9 14.6 5.4 UNS UNS 39.2 12.7 3.3 UNS UNS 37.8 10.8 UNS UNS UNS High (Bottom of Cap) 0 5 10 15 20 21 26 31 36 41 63.3 32.8 25.0 21.7 16.8 58.9 28.9 20.6 16.7 12.0 55.1 25.5 16.8 12.2 7.4 51.6 22.3 13.2 8.0 4.0 48.5 19.6 9.7 4.0 UNS 4 Low (Horiz. Strut) 0 5 10 15 20 21 26 31 36 41 57.4 30.0 23.0 19.9 15.4 53.7 26.4 18.9 15.3 11.0 50.3 23.3 15.3 11.1 6.8 47.2 20.3 12.1 7.3 3.5 44.3 17.8 8.9 3.6 UNS H = Bent height from top of bent cap to original ground line S = Scour depth, or original ground line minus new ground line UNS = unstable 121 Fig. 2.44. Unbraced, 1-Story X-Braced, and 2-Story X-Braced Bent Deformations 122 a. Ft loading at Bent Cap b. Ft loading at Horizontal Brace Fig. 2.45. GTSTRUDL Generated Deformations of 3-Pile Bent from Ft Loadings 123 a. Ft loading at Bent Cap b. Ft loading at Horizontal Brace Fig. 2.46. GTSTRUDL Generated Deformations of 4-Pile Bent from Ft Loadings 124 Table 2.29. Pushover Load, Ft, at Low Position for 2-Story X-Braced 3-Pile Bent of Height H=21 ft with HP10x42 Piles for Various Values of Horizontal Brace (HB) Stiffnesses Pushover Force, Ft (kips) P- Load (kips) No. of Piles H (ft) S (ft) H+S (ft) I = 0 A = 0 I = Ihb A = Ahb I = Ihb A = 2Ahb I = Ihb A=40Ahb I=1000 Ihb A = Ahb 60 3 21 0 5 10 15 20 21 26 31 36 41 43.9 17.6 9.5 UNS UNS 45.1 18.2 9.8 UNS UNS 45.3 18.2 9.8 UNS UNS 45.6 18.2 9.8 UNS UNS 45.1 18.2 9.8 UNS UNS 100 3 21 0 5 10 15 20 21 26 31 36 41 39.9 14.1 5.1 UNS UNS 41.0 14.6 5.4 UNS UNS 41.2 14.6 5.4 UNS UNS 41.4 14.6 5.4 UNS UNS 45.1 14.6 5.4 UNS UNS UNS = unstable I, A = values of I and A used in GTSTRUDL Pushover Analyses Ihb, Ahb = actual values of I and A of bent horizontal brace Pile Bent Parameters: 125 2.13 Additional Expansions of Applicability of the Tier-1 Screening Tool Guidelines for some additional expansions of applicability of the Phase II Report/Tier-1 Screening Tool are given below. 1. For pile bents with more than six HP steel piles in a row, do the following: Use the ?ST? as written for checking for pile/bent kick- out, plunging, and buckling failures. Use the pushover load check for the 6-pile bent in the ?ST? having the same HP pile size as the one being investigated to check the adequacy of bents with more than 6-piles in a bent. 2. For pile bents with HP steel piles larger than HP12x53 do the following: Use the ?ST? as written for checking the adequacy for kick-out and plunging failures, and use the Iy of the bent pile in checking for possible buckling when using the buckling equation of section three in the ?ST?. Use the pushover results for HP12x53 pile bents in checking the bent adequacy for pushover failure. 3. The current ?ST? checks for pile/bent ?kick-out? adequacy via checking to verify that depth of pile embedment in a firm soil after scour is equal to or greater than 3 ft. Upon reviewing this criterion further and recognizing the limited ability to accurately predict the Smax value at a bent site, it is recommended that the above criterion for ?kick-out? adequacy be retained as is in the Tier-2 ?ST?. 126 2.14 Closure Bent pushover loads for lower levels of P-loads, i.e., P=60k and 80k, and for a larger level of scour, i.e., S = 25 ft have been added in the refined ?ST?, and these have also been presented in terms of the critical scours, SCR. Bent pushover loads for cases of unsymmetric P-load distribution having only the upstream bridge lane loaded with live load have been added in the refined ?ST?. Pushover loads for cases of variable scour where the scour decreases in the downstream direction, and cases of unsymmetric P-load distribution and variable scour have also been added in the refined ?ST?. Checks have been made on the effect of additional pile axial load, ?P, due to lateral flood water loading, and checks regarding the adequacy of upstream bent piles when subjected to a debris raft loading at the level of horizontal strut for two-story bents have been made and included in this chapter. Also, the effect of height of debris raft loading on bent pushover, as well as the effect of continuous-span superstructures on bent pushover and pile buckling have been evaluated. Interestingly, the height of the debris raft loading has very little effect on the bent pushover load, and, as expected, continuous-span superstructures offer greater resistance to bent pushover failure. 127 CHAPTER 3: DETERMINING BRIDGE/BENT MAXIMUM APPLIED LOADS 3.1 General The maximum applied pile and bent gravity loads are primarily a function of: ? the span length ? the bridge width and girder spacing ? the superstructure support conditions, i.e., simply-supported or continuous-spans The procedures for determining maximum applied dead load (DL) are straightforward and rather easy to implement; however, the procedures for live load (LL) are more involved and not as easy to implement. In placing truck and lane loads in traffic lanes, the AASHTO design truck and lane loadings, seen in Fig. 3.1, are meant to cover a 10-ft. width. These loads are then placed in 12 ft. traffic lanes spaced across the bridge from curb-to-curb. If the curb-to-curb width is between 20 ft. and 30 ft., two design lanes are required, each of which is half the curb-to-curb distance. The number and spacing of design traffic lanes is based on the layout which creates the maximum stress. Table 3.1 shows the number of design lanes based on a bridge?s curb-to-curb width, and Fig. 3.1 128 illustrates ?truck lane loadings? and ?design lane loading? on a 32 ft. curb-to-curb width bridge. The larger of these two loadings is the required design live loading. It should be noted that the number of design traffic lanes and lane LL- loadings shown in Table 3.1 and Fig. 3.1 are appropriate for checking bent pile buckling or plunging, but are unrealistically conservative for the maximum high water level pushover loading unless the bridge actually has 3-traffic lanes. Otherwise, the LL-loading for the pushover loading check should be restricted to using the actual number of traffic lanes. Also, the most adverse LL-loading may occur with only the upstream lane loaded for the pushover loading condition, and this should be checked. Table 3.1 Design Traffic Lanes Curb to Curb Width No. of Lanes 20 to 30 ft. 2 30 to 42 ft. 3 42 to 54 ft. 4 54 to 66 ft. 5 66 to 78 ft. 6 78 to 90 ft. 7 90 to 102 ft. 8 102 to 114 ft. 9 114 to 126 ft. 10 129 Fig. 3.1 Live Load to Determine LLBent Max AppliedP 3.2 Determining Maximum Applied Dead Load Bridge girder maximum dead load reactions for various girder support conditions are summarized in Table 3.2 for a uniform dead load, ?DL. Table 3.2 Bridge Girder Maximum Reactions for SS and Equal Span Continuous Bridges Under Uniform Loads Bridge/Girder Support Condition DL MaxR LL MaxR SS 1.0 ?DL 1.0 ?LL 2-Span Continuous 1.25 ?DL 1.25 ?LL 3-Span Continuous 1.10 ?DL 1.20 ?LL 4-Span Continuous 1.15 ?DL 1.22 ?LL 5 -Span Continuous (or larger) 1.15 ?DL 1.22 ?LL 130 It should be noted that the tributary weight of the bent cap needs to be added to the appropriate girder reaction to determine the pile and bent design DL forces. If the bent cap size is known, that actual size is used in the ?ST? to determine the cap weight to add to the bent load. If the cap size is unknown, the following is assumed to estimate its size and weight. Girder/Pile spacing x (No. Piles ? 1) + 4 ft Bent Pile Cap Size = 2.5? x 2.5? x Cap Length Bent Cap Weight = Cap Size (volume in ft3) x 0.150 k/ft3 Assume Cap Weight Is Equally Distributed CapPile Cap WeightP No. Bent Piles= To Piles. Example problems illustrating the computation of DLMax AppliedP are given in Section 3.4. 3.3 Determining Maximum Applied Live Load As with the original ?ST?, an impact factor of 1.1 is assumed in determining the maximum applied pile live load(LL). Also, as with the original ?ST?, a girder- line approach is taken to estimate the maximum vehicular LL (plus impact) on a bent pile, and the approach is illustrated with its application to a simply-supported superstructure, with span lengths of 34? and a girder spacing of 6?, in Fig. 3.2. The loads shown in Fig. 3.2 apply to an HS20 loading and the loads shown in parenthesis pertain to an HS15 loading. LLMax AppliedP is the larger of those determined from the truck line load of Fig. 3.2(a) or the design lane loading of Fig. 3.2(b). 131 LL PileMax AppliedP is determined from Fig 3.2 and 3.3 as follows: a. Truck Line Load: SS Spans 2-Span Continuous LLPileP = ( ) ( )k k k20 2034 3416 + 16 + 4 1.1? ?? ? [ ]2(3.12)+16+9.36 1.1 =[ ] k16 + 9.41+ 2.35 1.1 = 30.5 k34.8 b. Design Lane Load: SS - Spans 2-Span Continuous LL kPile 2kP = 0.064 x6'x34'+26 1.1ft? ?? ? ? ? = [13.1+26]1.1 = 43.0 Governs [16.32+26]1.1=46.6k Governs LL kPileMax AppliedP = 43.0? for Simply Supported Bridge LL kPileMax AppliedP = 46.6? for 2-Span Continuous or Continuous for LL LL kPileMax AppliedP = 46.6? for 3 or More Span Continuous or Continuous for LL As can be seen from Table 3.2, for purposes of estimating the maximum LL Pile MaxP applied to a bent cap and pile, using the upper bound value of LL Max LLP =1.25w l would be appropriate for the ?screening tool? for equal-span continuous bridges of any number of continuous spans. Note also that the uniform lane loading (rather than truck wheel loadings) controls by a sizeable margin for both the SS bridge and the continuous bridges. [ ](0.064x6x34)1.25 + 26 1.1 132 Example problems illustrating the computation of LLPile MaxP are given in Section 3.4. Fig. 3.2 Girder Line Loading to Determine LLPile Max AppliedP Fig. 3.3 AASHTO H and HS Lane Loading 133 3.4 Example Bent Max AppliedP Determinations Two example problems illustrating the computation of BentMax AppliedP for purposes of checking bridge bent pushover adequacy in extreme flood/scour events are presented below. Both examples illustrate calculations of loadings for the symmetric case of both bridge traffic lanes loaded with LL, and for the unsymmetric case of only the upstream traffic lane loaded. Example 1 pertains to a 4-pile bent bridge and Example 2 pertains to a 3-pile bent bridge. Example 1: Refer to Figures 3.4 - 3.7 Fig. 3.4. 34? Span SS Bridge with 7? Deck, AASHTO Type II Girders (4 Girders at 8? Spacing), Jersey Barriers, 4-Pile Bents with 2.5? x 2.5? Caps AASHTO TYPE II GIRDERS 134 Determine BentMax AppliedP PDL: Deck: Deck Thickness x Out-to-Out Deck Width x Span Length x 0.150 k /ft.3 37' 32' 34' 0.150 / .12 kx x x ft = 95.2k Thickened Deck Overhang: ? Overhang Thickness x Overhang Width x Span Length x 0.150k /ft.3 32' 4' 34' 0.150 / . 212 kx x x ft x = 6.8k Diaph: 9'12 x Girder Depth x Distance Between Exterior Girders x 0.150k / ft.3 x No. Diaph/Span 39' 3.0' 24' 0.150 / . 312 kx x x ft x = 24.3k Girder: Girder Wt./ft x Span Length x No. Girders/Span 0.384 / . 34' 4k ft x x = 52.2k Barrier Rail: Jersey Barrier Wt./ft x Span Length x 2 0.390 / . 34' 2k ft x x = 26.5k Bent Cap: Cap Width x Cap Depth x Cap Length* x 0.150k / ft3 32.5' 2.5' 28' 0.150 / .kx x x ft = 26.3k *If Cap Length is not available use (Distance Between Ext. Girders + 4?) PDL = 231.3k 135 353.5 88.4 per pile . 4 piles= = = Bent k Max Applied kP No of Piles PLL ? Both Lanes Loaded (Case I Loading): Design Lane Load: 20.064 / . 10' 34' + 26.0 2 1.1? ?? ?k kft x x x = 105.1k Truck Lane Load: 20 2032 32 8 2 1.134 34? ?? ? ? ?+ +? ? ? ?? ? ? ? ? ?? ? k x = 122.2k?Governs PLL = 122.2k k k k DL LLP P 231.3 122.2 353.5? = + = + = Bent Max AppliedP ?P-load to be used above each pile in pushover analysis Fig. 3.5. Pushover Load Case I PLL ? Only Up-Stream Lane Loaded (Case II Loading): Design Lane Load: 20.064 / . 10' 34' + 26.0 1 1.1? ?? ?k kft x x x = 52.5k Truck Lane Load: 20 2032 32 8 1 1.134 34? ?? ? ? ?+ +? ? ? ?? ? ? ? ? ?? ? k x = 61.1k?Governs PLL = 61.1k 136 k Bent kDL DL Applied P 231.3P = =57.8 per pile No. of Piles 4= k Bent kLL LL Applied P 61.1P = =30.6 2 2= ; Bent LL AppliedP = 0 (other 2 piles) 88.4k 57.8k Fig. 3.6. Pushover Load Case II Note, Therefore, based on Example 1, in performing pushover analyses for Load Case II, use the following bent loadings. Fig. 3.7. Unsymmetric P-Loading for 4-Pile Bents 88.4 57.8 = 1.53 or 1_ 1.53 = 0.65 137 Example 2: Refer to Figures 3.8 - 3.11 Fig. 3.8. 34? Span SS Bridge with 7? Deck, AASHTO Type II Girders (3 Girders at 8? Spacing), Jersey Barriers, 3-Pile Bents with 2.5? x 2.5? Caps Determine BentMax AppliedP PDL: Deck: Deck Thickness x Out-to-Out Deck Width x Span Length x 0.150k /ft.3 37' 27' 34' 0.150 / .12 kx x x ft = 80.3k Thickened Deck Overhang: ? Overhang Thickness x Overhang Width x Span Length x 0.150k/ft.3 32' 4' 34' 0.150 / . 212 kx x x ft x = 6.8k Diaph: 9'12 x Girder Depth x Distance Between Exterior Girders x 0.150k / ft.3 x No. Diaph/Span 39' 3.0' 16' 0.150 / . 312 kx x x ft x = 16.2k AASHTO TYPE II GIRDERS 138 310.0 103.3 per pile . 3 piles= = = Bent k Max Applied kP No of Piles Girder: Girder Wt./ft x Span Length x No. Girders/Span 0.384 / . 34' 3k ft x x = 39.2k Barrier Rail: Jersey Barrier Wt./ft x Span Length x 2 0.390 / . 34' 2k ft x x = 26.5k Bent Cap: Cap Width x Cap Depth x Cap Length* x 0.150k / ft3 32.5' 2.5' 20' 0.150 / .kx x x ft = 18.8k *If Cap Length is not available use (Distance Between Exterior Girders + 4?) PDL = 187.8k PLL = Both Lanes Loaded (Case I Loading): Design Lane Load: 20.064 / . 10' 34' + 26.0 2 1.1? ?? ?k kft x x x = 105.1k Truck Lane Load: 20 2032 32 8 2 1.134 34? ?? ? ? ?+ +? ? ? ?? ?? ? ? ? ? ? k x = 122.2k?Governs PLL = 122.2k k k k DL LLP P 187.8 122.2 310.0? = + = + =BentMax AppliedP ?P-load to be used above each pile in pushover analysis Fig. 3.9. Pushover Load Case I 139 PLL ? Only Up-Stream Lane Loaded (Case II Loading): Design Lane Load: 20.064 / . 10' 34' + 26.0 1 1.1? ?? ?k kft x x x = 52.5k Truck Lane Load: 20 2032 32 8 1 1.1 34 34 ? ?? ? ? ?+ +? ? ? ? ? ?? ? ? ?? ?k x = 61.1k?Governs PLL = 61.1k k Bent kDL DL Applied P 187.8P = =62.6 per pile No. of Piles 3= k Bent kLL LL Applied P 61.1P = =30.6 2 2= ; Bent LL AppliedP = 0 (other 1 pile) 93.2k 62.6k Fig. 3.10. Pushover Load Case II Note, 93.2 1 = 1.49 or = 0.6762.6 1.49 k k Therefore, based on Example 1 and 2, in performing pushover analyses for Load Case II, use the following bent loadings. Fig. 3.11. Unsymmetric P-Loading for 3-Pile Bents 140 CHAPTER 4: REFINED ?ST? AND TIER-2 SCREENING 4.1 General The original ?screening tool? developed to assess the adequacy of bridge pile bents for extreme flood/scour events screened only steel HP pile bents where the piles were HP10x42 or HP12x53, and checked these bents for the following possible failure modes: 1. Bent pile tip ?kick-out? failure (due to insufficient pile embedment after scour) 2. Bent pile plunging failure (due to insufficient pile end bearing or side friction capacity after scour) 3. Bent pile buckling failure (due to insufficient pile buckling capacity after scour) 4. Bent pushover failure (due to the combined effect of gravity P- loads and lateral flood water loads on the bent after scour) In checking the many bent geometries and loading scenarios and piling bracing and support conditions, simplifying assumptions were made to estimate both the maximum applied loads on the bent/pile, and the load capacities of the bent/pile. In developing the ?ST?, upper or lower bound values as appropriate for the bent 141 parameters were sometimes used, and in cases of uncertainty, which were many, conservative values were used. After using the ?ST? for about a year now, areas for improvements and refinements of the ?ST? have been identified, as well as other possible critical load conditions and failure modes. These improvements in the basic ?ST? have been incorporated in the refined/2nd-edition ?ST? which is presented and discussed in the following section. This new edition still incorporates a conservative approach where uncertainties exist. Also included in this chapter is a section on 2nd-tier screening which should be performed to address the ?blocks? in the original ?ST? that instructed the user to ?check more closely for possible failure?. This 2nd-tier screening should result in additional bents being determined as adequate for extreme flood/scour events, and thus should further reduce the number of bents requiring a fully comprehensive analysis to assess the bent?s adequacy. 4.2 Refined/2nd Edition ?ST? The refined/2nd edition ?ST? is shown in flowchart form in Fig. 4.1. By comparison of this figure with the corresponding one for the original ?ST?, one can readily see that an additional failure-check module, i.e., Module 5, has been added to the refined/2nd edition ?ST?. This module provides for a check of the upstream bent pile for possible failure as a beam-column when simultaneously subjected to an axial P-load and a lateral flood water loading on a debris raft located with its top 7.5 ft below the top of the bent cap, i.e., with the Ft loading 142 located 9.5 ft below the top of the bent cap. This check and module is discussed later in this section. Also, one can note in Fig. 4.1 that no changes were made in the Preliminary Evaluation Module, i.e., in Block 1. An enlarged drawing of Block 1 only is shown in Fig. 4.2 for convenience and readability. In the ?Kick-Out? and Plunging Evaluation Module (Block 2), slight refinements in the wording and sequence for indicating the adequacy of bent piles for ?kick-out? were made at the very beginning of the Block. However, no changes of substance were made in checking for ?kick-out?, nor are any follow-up screenings indicated for those bents where ?check more closely for ?kick-out? failure? is indicated by the ?ST?. However, in this module, if a plunging failure is identified as being possible, the user is referred by the ?ST? to second-tier screenings (Tier-2/2) to make assumptions regarding the bent pile-driving system when complete information on the system is not known, and/or to further refine the maximum load on the bent and pile in assessing the adequacy of the bent/pile for plunging. An enlarged drawing of Block 2 only is shown in Fig. 4.3 for convenience and readability. 143 Fig. 4.1. Refined Screening Tool Flowchart for Assessing Pile Bent Adequacy During an Extreme Flood/Scour Event 144 Fig. 4.2. Enlargement of Preliminary Evaluation Module 145 Fig. 4.3. Enlargement of Kick-Out and Plunging Evaluation Module 146 Block 3 of the Refined ?ST?, the Buckling Evaluation Module, is shown in enlarged form in Fig. 4.4. The refinements allow bent buckling adequacy to be assessed for all steel HP pile bents with piles in a single row for any number and size of pile and any depth of embedment after scour in excess of 3 feet. As with the original ?ST?, Figs. 4.5a and 4.5b provide labeled dimension values and member definitions including members HB1 and HB2 referred to in Fig. 4.4. Note that Block 3 has been slightly modified to use the parameter X (distance from top of bent cap to lowest horizontal brace) in determining the position of the lowest horizontal brace rather than the parameter ?E? and 4 ft. Block 4 of the Refined ?ST?, the Bent Pushover Evaluation Module, is shown in enlarged form in Fig. 4.6. The refinements in this module are the most sweeping and significant of all. In refining the ?ST? pushover load assessment during this Phase III work, the effects of additional P-load levels and distributions, scour levels and distributions, and height of pushover loading on bent pushover adequacy were performed via evaluation of bent pushover loads for these conditions using GTSTRUDL. These new pushover load evaluations are shown in tables and figures in Chapter 2. A user of the ?ST? can continue to use the original ?ST? in evaluating bent pushover adequacy and still be conservative. However, the additional pushover load tables generated in this Phase III work provide a more accurate assessment of pushover adequacy under a larger range of bridge/bent conditions. As can be seen in Fig. 4.6, the refined Block 4 identifies at the beginning a condition of no bent debris raft forming and proceeds to show the pushover 147 Fig. 4.4 Enlargement of Refined Buckling Evaluation Module 148 Fig. 4.5a. Typical ALDOT X-Braced Pile Bent Geometry 149 X=Vertical Distance in Feet From Top of Bent Cap To the Lowest Horizontal Brace (HB) Buckling Mode 1 - Nonsidesway (assuming bracing members buckle and piles have a 50% fixity at the cap and ground) 2 1 2 1 CR1 CP y CR EIpi? l where 1crl = S+?H?-1? (4.1) Buckling Mode 2 - Sidesway (lower portions of piles) 2 2 2 2 CR2 CP y CR EIpi? l (4.2) Where: 2crl =S+(?H?-X) for 1 or 2-story bent if member HB1 is present and for 2-story bent if only member HB2 is present 2crl =S+(?H?-1?) for 1-story bent if HB1 is not present and for 2-story bent if HB1 and HB2 are not present Fig. 4.5b. Transverse Buckling Modes and Equations for X-Braced Bents 150 Fig. 4.6. Enlargement of the Bent Pushover Evaluation Module 151 check for this condition. Also, the refined Block 4 identifies two 2nd tier screenings (Tier-2/4A and Tier-2/4B) for bents that do not successfully pass through the original ?ST?. By executing these refinements, it is anticipated that many more bents will be determined to be adequate without requiring full-blown structural stability analyses. As indicated earlier, Block 5 has been added to the refined/2nd edition ?ST? and is shown in enlarged form in Fig. 4.7. This module involves a check for possible failure of the upstream pile as a beam-column due to a combined axial P-load and a lateral flood water loading, Ft, acting on a debris raft formed at an elevation of 9.5 ft below the top of the bent cap (see Fig. 2.36). It should be noted that if the debris raft forms at or near the top of the bent, then bent pushover failure would govern. If the bent is X-braced, the bracing will serve to distribute the force Ft to all of the piles in the bent and the piles and bent will be adequate for the lower position of the Ft load. Also, if the bent piles are HP piles larger than HP10x42, then the upstream pile will be safe for the beam-column loading. Thus, the possibility of a beam-column failure of the upstream bent pile only occurs when the bent piles are ? HP10x42 or smaller ? Unbraced ? Loaded with the Ft loading at an elevation of 9 ft or more (debris raft forming at elevation 7 ft or more) below the top of the bent cap. 152 Fig. 4.7. Enlargement of Upstream Pile Beam-Column Evaluation Module 153 These conditions are included in Block 5 which, for conditions where a beam- column failure is possible, guides the user through a determination of the Sfailure level and then a conversion of this value to a safemaxS by dividing Sfailure by a F.S.=1.25. In turn, safemaxS is compared with the Smax anticipated at the site to determine the adequacy of the upstream bent pile as a beam-column. 4.3 Second Tier/Tier-2 Screening As indicated in the previous section, ? there are no 2nd tier screening referrals in the Preliminary Evaluation Module, 1. ? there are two 2nd tier screening referrals each in Modules 2 and 4, and these are shown shaded in gray in the 2nd Edition ?ST? flowcharts of Fig. 4.3 an 4.6. ? 2nd tier screenings initially identified for Module 3 were combined with 1st tier screenings of the original ?ST? into a new refined Module 3 which is shown in Fig. 4.4. Each of these 2nd tier screenings, as well as the new refined Module 3 (Buckling Module) are presented and discussed below. 4.3.1 Pile Plunging Evaluation 2nd Tier Screening Second-tier pile/bent plunging screenings are recommended for the shaded/gray referral blocks in the ?ST? Flowchart shown in Module 2 in Figs. 4.1 and 4.3. Second-tier screening for bents for which complete information about the bent pile-driving system are not known, i.e., Tier- 2/2A screening, is 154 described in Fig. 4.8a. In this second-tier screening, the most conservative or most probable conservative values of the missing information are assumed, and the user is returned to continue executing the ?ST?. Second-tier screening for bents that do not pass the Scr ? Smax check in the pile plunging evaluation, i.e., Tier-2/2B screening, are described in Fig. 4.8b. In this second tier screening, a new and probably less conservative pilemax appliedP is determined for the pile being investigated. It should be noted that after executing the Tier-2/2 screenings, the user should return to, and continue executing, the ST. 4.3.2 Pile Buckling Evaluation 2nd Tier Screening Second-tier screenings were initially added to the buckling evaluation module, i.e., Block 3, to allow expanded screening for additional sizes of HP pile bents, numbers of HP piles, and depths of pile embedment after scour. However, this procedure was later changed to combining the 2nd tier and 1st tier screenings into just one buckling evaluation module, i.e., the refined Block 3 screening which is shown in Figs. 4.1 and 4.4. The refined buckling evaluation module allows bent buckling adequacy evaluation for all steel HP pile bents with any number of piles in a single row, and for any depth of pile embedment after scour in excess of 3 feet. It should be noted that if the depth of embedment after scour, ?as, is less than or equal to 3 feet, then the ?ST? will indicate a possible ?kick-out? failure may occur. If the bent is determined to be adequate for buckling, then the refined ?ST? moves forward to checking the bent adequacy for pushover failure. 155 If lack of information regarding the bent pile driving system in Block 2 of the ?ST? causes exit of the ST to Tier-2/2A ST check, do the following: ? If driving resistance at end of driving (EOD) is unknown, assume a Final Driving Resistance = 5 blows/inch. ? If type of driving hammer and hammer driving energy is unknown, assume a 6 ft-kip hammer driving energy. ? If it is unknown whether piles are primarily ?End Bearing? or ?Friction?, assume the piles are primarily ?Friction Piles?. ? After making one or all of the assumptions above, return to the ST at the point/block of exit and continue executing the ST. Fig. 4.8a. Tier-2/2A Screening for Pile Plunging Adequacy Assessment 156 In recognition of the facts that, ? the most heavily loaded pile in a bent will get ?lean-on? plunging support from the adjacent piles in the bent ? for continuous span bridges, the most heavily loaded bent will get ?lean-on? support from the adjacent supports/bents ? the loading of all possible Design Traffic Lanes (see Table 3.1 in Phase III-Screening Tool Users Guide) with LL when a bridge only has two actual traffic lanes is unreasonable for an extreme flood/scour event it is recommended that pilemax appliedP be redetermined as follows: ? Assume each bridge span supported by the bent under investigation is a SS span loaded with LL on only the bridge actual traffic lanes. ? Determine Bentmax appliedP based on the assumption above ? Assume Bent max appliedpile max applied PP = No. Piles Return to the ST at the point/block shown in Fig. 4.1 and continue executing the ST. Fig. 4.8b. Tier-2/2B Screening for Pile Plunging Adequacy Assessment 157 4.3.3 Bent Pushover Evaluation (Block 4) 2nd Tier Screening Second-tier bent pushover screenings are recommended for the shaded/gray referral blocks in Block 4 of Fig. 4.1. The 2nd tier screening regarding the number and size of the bent piles, i.e. Tier-2/4A screening, is given in Fig. 4.9a. Second-tier screening for bents that do not pass the Scr > Smax check in the bent pushover evaluation, i.e., Tier-2/4B screening, is described in Fig. 4.9b. It should be noted in Fig. 4.8b that, for continuous bridges, the lateral flood water loading acting on a bent is reduced, and thus the pushover capacity of the bent can likewise be reduced and still be adequate. The bent pushover capacities for various continuous-span superstructures are given in Section 2.4 of this report. 4.4 Closure In this Phase III work, improvements and refinements in the ?ST? have been made and are included in the refined/2nd edition ?ST? presented in Section 4.2. It should be noted in Section 4.2 that an additional possible mode of bent failure and a check for the same, i.e., failure of the upstream bent pile as a beam- column, has been added to the ?ST?. This failure mode is only possible for unbraced bents with HP10x42 or smaller piles where the lateral flood water loading, Ft, can be applied at an elevation of 9 ft or more below the top of the bent cap. The author views this 2nd edition ?ST? as being the basic ?ST? that should be applied to all of ALDOT?s steel pile bent supported bridges that are exposed to extreme flood/scour events. 158 If the bent is not a 3, 4, 5, or 6-pile bent with or without X-bracing with HP10x42 or HP12x53 piles, do the following: ? Bents with more than 6 HP piles of any size in a row, whether braced or unbraced, have adequate pushover capacity for maximum scour levels anticipated anywhere in Alabama, and thus are safe for pushover. ? For bents with HP10x57 piles, check the bent pushover adequacy by treating it as a HP10x42 pile bent. ? For bents with HP12x(63, 74, 84) or larger HP piles, check the bent pushover adequacy by treating it as a HP12x53 pile bent. ? Bents with piles as large or larger (based on the pile Iyvalue), than HP12x53 with 5 or more piles have adequate bent pushover capacity for the maximum scour levels anticipated anywhere in Alabama, and thus are safe for pushover. Fig. 4.9a Tier-2/4A Screening for Bent Pushover Adequacy Assessment 159 For bents not passing the Scr > Smax requirement for pushover adequacy, do the following: a. Use the expanded bent pushover capacity tables and information in Chapter 2, i.e., ? Pushover loads for nonuniform scour distribution ? Pushover load for debris raft at lower height level on the bent ? Reduced flood water loading due to no debris raft forming ? Reduced lateral load due to a continuous superstructure as appropriate to determine more refined values of both, the maximum applied lateral load on the bent, and the bent pushover capacity. b. Check to see if, max applied capacityt tF 1.25 F? ? a2cornerleftup F.S. c. If max applied capacityt tF 1.25 F? ? , the bent is adequate for pushover. If max applied capacityt tF 1.25 > F? , the bent is not adequate and should be checked more closely for possible pushover failure. Fig. 4.9b Tier-2/4B Screening for Bent Pushover Adequacy Assessment 160 For those bridges/bents with steel HP pile bents that failed to pass the original ?ST? screening process because of pile size or number of piles in the bent, and for the steel HP pile bents that fail to pass the ?ST? screening process for a lack of adequate capacity in the areas checked by the ?ST?, the second tier, or Tier-2, screening process developed in this work should be applied. This Tier- 2 screening process is presented in Section 4.3. Only those bridges with steel HP pile bents that did not check out to be adequate via the original ?ST? should be subjected to this second tier or Tier-2 screening. Bents not checked via the ?ST? to date, should be checked using the Phase III refined ?ST?. It is anticipated that the Tier-2 screening will find many of the bridges/bents that failed to pass the initial ?ST? to be adequate. Those bridges/bents not found to be adequate via the follow-up Tier-2 screening should be analyzed more closely via a comprehensive structural stability analysis for the maximum flood/scour event that can occur at the bridge site. 161 CHAPTER 5: EXAMPLE APPLICATIONS OF THE TIER-2 ?ST? 5.1 General As indicated in Chapter 4, there are no 2nd tier screening referrals in the original or refined ?ST? in the Preliminary Evaluation Module (Module 1), and thus there are no Tier-2 screenings for this module. Also, in the Kick-Out and Plunging Evaluation Module (Module 2), there are no changes in the ?ST? regarding the check for ?kick-out? failure and there are no Tier-2 screenings for those piles/bents identified as possibly having a ?kick-out? failure problem. However, for piles/bents identified in the refined ?ST? as possibly having a pile plunging or a bent pushover failure problem, the refined ?ST? refers the user to a 2nd level of screening, i.e., Tier-2 screening, in checking for these possible failure modes. As indicated earlier, for pile buckling checks, 2nd level screenings have been implicitly incorporated into the buckling evaluation module, and thus, there are no explicit Tier-2 screenings for buckling. It is anticipated that the Tier-2 screenings will be able to determine that many of the piles/bents sent to this 2nd level of screening are adequate and do not need to be checked further. The original ?ST? Reports included example checks for failure via pile plunging, pile buckling, and bent pushover. In the following sections, example applications are given for the refined ?ST?, Tier-2 plunging and pushover failure 162 checks, and for checking of the upstream pile for possible failure as a beam- column. These examples focus on the Tier-2 screening process. They are designed to assist a user starting at a point at which the original ?ST? has indicated that ?the piles/bent should be looked at more closely for a possible failure?. The Tier-2 screening constitutes the first step, and in many cases the only step needed, in the ??bent should be looked at more closely?? process. 5.2 Bent/Site Conditions to Check for Need/Applicability of the ?ST? Just as with the original ST, the questions below should be answered at the very beginning to determine the need to apply the Refined ST, or to determine the applicability of the Refined ST to the bridge bent/site under investigation. In certain situations, the Refined ST refers the user to Tier-2 screenings. Also, it should be noted that Question 4 below expands the range of applicability of the Refined ST to all steel HP pile bents. 1. Is the bridge over water or in a flood plain where it may become over water during an extreme flood? If answer is No, the bridge bents do not need to be checked by the ST. 2. Is the bridge at a site where the maximum estimated scour, Smax, is max0 3S ft? ? ? If answer is Yes, the bridge bents do not need to be checked by the ST. 3. Is the bridge at a site where the maximum estimated scour, Smax, is greater than the pile embedment length, bgl , i.e., is max bgS ? l ? 163 If the answer is Yes, the bridge pile/bent will have a pile/bent ?kick-out? or plunging failure and there is no need to check with the ST. Immediate corrective action should be taken. 4. Are the bridge pile bents 3, 4, 5, 6, 7, 8-pile (or more) bents with piles in a single row with or without X-bracing and with the piles being steel HP piles? If the answer is No, the bridge bents cannot be checked by the ST. 5.3 Example Applications for Tier-2 Pile Plunging Failure Check Given below are some example applications of the refined/2nd edition ?ST? checks for possible pile/bent plunging and kick-out failures. It should be noted that the refined ?ST? is the same as the original ?ST? regarding checking for pile/bent ?kick-out? failure, i.e., checking to make sure that the bent piles have more than 3 ft of embedment in a firm soil after scour to be safe from a kick-out failure. However, for the pile plunging check, the refined ?ST? includes two Tier-2 pile-plunging checks, and these are emphasized in Examples 1 and 2 below. 164 Fig. 5.1. Example Problem 1 for Kick-Out and Plunging 165 Fig. 5.2. Example Problem 1 for Kick-Out and Plunging (Continued) 166 Fig. 5.3. Example Problem 1 for Kick-Out and Plunging (Continued) 167 Fig. 5.4. Example Problem 2 for Plunging 168 Fig. 5.5. Example Problem 2 for Plunging (Continued) 169 Fig. 5.6. Example Problem 2 for Plunging (Continued) 170 Fig. 5.7. Example Problem 2 for Plunging (Continued) 171 Fig. 5.8. Example Problem 2 for Plunging (Continued) 172 Fig. 5.9. Example Problem 2 for Plunging (Continued) 173 5.4 Example Applications for Tier-2 Pile Buckling Failure Check Applications of the refined ?ST? buckling check are given in Examples 3, 4, and 5 below. The examples focus on using the expansions and refinements made in the refined ?ST? buckling check module. As indicated earlier, 2nd-tier screening has been implicitly included in the refined buckling check module. 174 Fig. 5.10. Example Problem 3 for Buckling 175 Fig. 5.11. Example Problem 4 for Buckling 176 Fig. 5.12. Example Problem 5 for Buckling 177 5.5 Example Applications for Tier-2 Bent Pushover Failure Check Four example applications of the refined ?ST? bent pushover check are given below. The refined ?ST? bent pushover check includes several new tables/features that were not available in the original ST such as, ? Lower P-load levels of P=60k and 80k acting on the cap ? Reduced P-load levels on the downstream side of bent ? Reduced level of scour in the downstream direction of the bent ? A debris raft not forming at the bent ? A debris raft forming at a lower level on the bent The refined ?ST? also includes two Tier-2 pushover screening checks. Example Applications 6, 7, 8 and 9 below focus on the Tier-2 screening checks as well as on some of the new tables/features mentioned above. 178 Fig. 5.13. Example Problem 6 for Pushover 179 Fig. 5.14. Example Problem 6 for Pushover (Continued) 180 Fig. 5.15. Example Problem 7 for Pushover 181 Fig. 5.16. Example Problem 7 for Pushover (Continued) 182 Fig. 5.17. Example Problem 8 for Pushover 183 Fig. 5.18. Example Problem 8 for Pushover (Continued) 184 Fig. 5.19. Example Problem 9 for Pushover 185 Fig. 5.20. Example Problem 9 for Pushover (Continued) 186 Fig. 5.21. Example Problem 9 for Pushover (Continued) 187 Fig. 5.22. Example Problem 9 for Pushover (Continued) 188 5.6 Example Application for Bent Upstream Pile Beam-Column Failure Check Example 10 is an example application of the refined/2nd edition ?ST? checking for possible failure of a bent?s upstream pile as a beam-column from a combined axial P-load and a lateral loading on a debris raft forming at an elevation of 7.5 ft below the top of the bent cap, and thus applying the Ft loading at 9.5 ft below the top of the bent cap. This mode of pile/bent failure was not checked in the original ?ST?. 189 Fig. 5.23. Example Problem 10 for Beam-Column 190 5.7 Closure Section 5.2 identifies four questions which must be answered at the very beginning of a ?check? to determine the applicability and/or need to apply the ST to determine a bent?s adequacy. It should be noted that Question 4 in Section 5.2 expands the range of applicability of the Refined ST to include all steel HP pile bents. Example applications of the ST are given in Sections 5.3-5.5 of checks for bent failure via pile plunging, pile buckling, and bent pushover. These examples illustrate some of the expansions of load conditions, load levels, bridge span support conditions, symmetry of loading and/or scour conditions, etc. included in the Refined ST. The examples emphasize applications of the Tier-2 screening process. Section 5.6 provides an example application check of a bent?s upstream pile for a possible beam-column failure due to a combined axial P-load and a lateral flood water loading, Ft, from a debris raft. This failure check is an addition in the refined/2nd edition ?ST?. 191 CHAPTER 6: CONCLUSIONS AND RECOMMENDATIONS 6.1 General In Phase II of this research, a ?screening tool? (ST) was developed to assess the adequacy of bridge pile bents for bents with HP10x42 and HP12x53 steel piles for estimated extreme flood/scour events. The ST has been used in manual form by ALDOT bridge maintenance engineers for the past year and appears to be working nicely. The purposes of this Phase III work were to take the ?screening tool? developed in Phase II and ? simplify and refine it ? extend and expand its scope of applicability ? develop a second-tier of screening to use as a follow-up for those cases where the ?ST? indicates, ?Bent should be looked at more closely for possible plunging, buckling, or push-over failure?. ? develop an automated version of the ?ST?. These purposes were the focus of Phase III research work, and conclusions and recommendations based on this work are presented in the following sections. It 192 should be noted that a separate Phase III thesis was prepared for the last purpose listed above. The automated ?ST?, along with example applications and conclusions and recommendations pertaining to the automated ?ST? are presented in that thesis and are not included herein. 6.2 Conclusions A number of questions pertaining to the effect of additional loading conditions, scour conditions, height of application of a debris raft pushover load, unsymmetric bridge LL, continuous superstructures, etc., on possible bent failure during an extreme flood/scour event have surfaced since submission of the Phase II Report. Most of these questions required additional bent failure analyses, and these are presented in Chapter 2. A summary of the most important of these analyses and their results are presented below. 6.2.1 Additional Pile Axial P-load Due to Flood Water Lateral Loading Analyses that were undertaken to determine these additional P-loads (?P- loads) are presented in Section 2.3. In each case, the tallest possible bent (?H? = 25 ft) with the maximum scour (S = 25 ft) was considered. Only in the case of a 3-pile bent was the ?P viewed as being significant (?P = 15.6k on the downstream batter pile). This additional axial load would contribute to trying to plunge or buckle the downstream pile. However, this pile would get some ?lean- on? support from the other piles in the bent. Also, the ??P at a bent would be zero and thus their effect on the bent pushover force would be minimal, so the additional P-load need not be considered when determining P-loads acting on a pile bent. 193 6.2.2 Effect of Continuous Spans on Bent Pushover Analyses were undertaken to determine the flexural stiffness of a typical bridge deck/curb system bending in its horizontal plane and of a typical 3-pile or 4-pile bent bending in its vertical plane in Section 2.4. From these analyses it was determined almost all of the lateral deflection due to a debris raft Ft loading is due to flexing of the bent piles. Thus, assuming a rigid superstructure, it was determined that Bentmax applied t1F = FN ? where Ft = flood water load on debris raft N = number of continuous spans If this Bentmax appliedF < pushover capacitytF (given in Tables in this report) then the bridge/bent is safe from a pushover failure. 6.2.3 Effect of Continuous Spans on Bent Pile Buckling Piles/bents supporting continuous span superstructures, or those made continuous for LL, cannot buckle in a sidesway mode unless the entire continuous segment does. This would require an unrealistically large loading and thus the piles/bents cannot buckle in a sidesway mode. For the tallest ALDOT bents (?H? = 25 ft) subjected to the largest anticipated scour (S = 25 ft), the pile ?max would be ?max = ?H? + S ? 1? = 25 +20 ? 1 = 44 ft For this case, if, 194 Pmax applied ? 118k for an HP10x42 pile Pmax applied ? 209k for an HP12x53 pile then the pile/bent is safe from buckling. If Pmax applied is larger than the above values, the pile/bent may still be safe depending on the bent height and level of scour at the site. In this case, the bent should be checked for buckling in the manner outlined in the ?ST?. 6.2.4 Bent Pushover Loads for Smaller P-load Levels Pushover loads in the Phase II ?ST? were determined for various bent geometries, pile sizes, scour levels, and bracing conditions for P-loads (one applied to the bent cap above each pile) of {P} = {100k, 120k, 140k, 160k}. However, for some smaller bridges, the P-loads are sometimes only approximately 80k. In these cases, the ?ST? can be used with the P = 100k results, but this yields results that are too conservative. Thus to expand the range of accurate applicability of the ?ST?, additional pushover analyses were performed for 3-pile and 4-pile bents for P-loads of {P} = {60k, 80k}. These are presented in Section 2.6. The P = 60k level was added in light of allowing checks of cases where the LL is only applied to the upstream traffic lane, and also because it would allow interpolation of results for uniform P-loads somewhat less than 80k. 6.2.5 Pushover Loads for Unsymmetric P-load Distribution Pushover analyses in the Phase II ?ST? assumed a uniform P-load distribution across the bent cap, as indicated in the subsection above. These analyses, along with the additional smaller P-load levels of the previous 195 subsection, produced pushover analyses results for a uniform P-load distribution for P-loads of {P} = {60k, 80k, 100k, 120k, 140k, 160k}. However, it was not clear that a uniform P-load distribution yielded a smaller bent pushover load, Ft, than an usymmetric P-load distribution, even though it provided the larger gravity bent loading. It was reasoned that a smaller unsymmetrical P-load distribution on a bent, resulting from the LL being only applied to the upstream traffic lane, may result in a smaller pushover load. From earlier work, it was concluded that pushover failure was only a problem with the narrow-width 3-pile and 4-pile bents, thus these two pile bent configurations were considered when checking the pushover loads for unsymmetric P-load distribution. The results of pushover analyses for the 3- and 4-pile bents with unsymmetric P-loads are presented in Section 2.7, and the bent pushover load for these loadings turned out to be a little smaller in every case than the corresponding bent with a uniformly distributed P-load. Figures 2.26 ? 2.29 graphically illustrate the small difference in pushover load between the unsymmetrical and symmetrical P-loading cases. Even though the unsymmetrical distribution gives somewhat smaller pushover loads, and earlier screenings via the Phase II ?ST? assumed a uniform P-load distribution, the fact that the difference in pushover load between the two P-load distributions is quite small and that actual scour distributions are not uniform, as earlier assumed, which leads to somewhat conservative estimates of pushover capacities (see the next subsection), the net effect of these two factors offset each other and the earlier pushover analyses assessments are felt to be reasonable and accurate. 196 6.2.6 Pushover Loads for Variable Scour Distribution The Phase II ?ST? assumed a uniform scour of a given magnitude over the full width of the pile bent being analyzed, and this leads to smaller bent pushover loads than would occur if the scour decreased in the direction of river flow along the width of the bent. The effect of variable scour along the width of a pile bent was analyzed for 3- and 4-pile bents in Section 2.8, and the results are shown in Section 2.8. Figures 2.33 and 2.34 reflect the greater pushover capacity that a bent has if the scour decreases from its maximum value in the direction of river flow, as opposed to the case where the scour remains at its maximum value over the full width of the bent. Figure 2.35 shows plots of pushover force, Ft, vs. bent height plus scour, H+S, for cases where both unsymmetrical P-load and variable scour occur together and reflects a greater pushover capacity for this case when compared to that of a uniform P-load and uniform scour case. 6.2.7 Effect of Vertical Location of Debris Raft on Bent Pushover In the Phase II work and ?ST?, the debris raft on which the horizontal flood water loading, Ft, acts was assumed to be configured such that the top of the raft was at the height of the top of the bent cap. This placed the Ft loading at the bottom of the bent cap, which was viewed as the worst case position in checking bent pushover failure. This would be the case if the bent acted as a rigid body and exhibited rigid body tip-over failure, or if the bent is an unbraced frame with only bending in the plane of the frame about the pile weak axes. For situations where the topology at the bridge location is such that the high water level is 197 significantly lower than the top of the bent cap, it was anticipated that the Phase II assumptions were overly conservative. In the Phase III work, pushover analyses were performed for 3- and 4-pile bents with the debris raft water loading, Ft, applied at the location of the bottom of the X-bracing for single-story bents and at the height of the horizontal strut located between the upper X-bracing and lower X-bracing for 2-story bents. A description of this work and its results are presented in Section 2.12. It was anticipated that this loading location would yield larger pushover loads and would thus allow some bents previously classified as inadequate for pushover loading to be reclassified as adequate. However, the analyses results essentially indicated that the vertical position of the flood water loading, Ft, doesn?t significantly affect the bent pushover load. The bent bracing system is effective in maintaining the relative geometrical relationships of the bent members in the region(s) of the X-bracing, and almost all of the bending deformations of the bent occur in the lower unbraced (after scour) region and is essentially independent of the location at which Ft is applied in the upper braced region of the bent. Figures 2.44 ? 2.46 in Section 2.12 show good graphical bent deformation illustrations of this. 6.2.8 Bent Upstream Pile as Beam-Column It should be noted that for the lower position of the flood water loading, Ft, the upstream bent pile was checked for adequacy in an unbraced bent assuming it acts as a beam-only member and as a beam-column member. These checks are shown in Section 2.11. In all situations, the upstream pile is adequate when 198 checking as a beam-only member. When checking the upstream pile as a beam- column (which it is), the pile is adequate for all situations if it is an HP12x53 pile. However, when it is an HP10x42 pile, the pile may not be adequate when the scour, S > 12 ft, depending on the original height ?H?, of the bent. The results of the analyses summarized above have been included in the improvements and refinements made in the ?ST? during this Phase III work. The resulting Refined/2nd Edition ?ST? is discussed and presented in flowchart form in Chapter 4 and Fig. 4.1. Also, a section on 2nd-tier screening (Section 4.3) is included in this report; this 2nd-tier screening should be performed to address the ?blocks? in the refined/2nd edition ?ST? which indicate that the user should ?check more closely for possible failure?. These Tier-2 screening referrals are shown shaded on the refined ?ST? flowchart of Fig. 4.1. The 2nd tier screenings should result in additional bents being determined as adequate for extreme flood/scour events, and thus should further reduce the number of bents requiring a fully comprehensive analysis to assess the bent?s adequacy. A discussion of the automation of the ?ST?, the automated ?ST?, and example applications of the automated ?ST? are not presented herein, but rather are given in a separate thesis. 6.3 Recommendations Readers interested in the workings of the refined/2nd edition ?ST? and that plan to use it as a work tool to screen pile bent-supported bridges to assess their adequacy for extreme flood/scour events should recognize and do the following: 199 ? The ?ST? is a screening tool to determine the adequacy of steel HP pile bridge bents for an estimated extreme flood/scour event. ? The ?ST? checks for possible HP pile/bent failure via - pile ?kick-out? due to insufficient pile embedment after scour - pile plunging due to insufficient soil bearing tip bearing and side friction capacity - pile buckling - bent pushover due to flood water lateral loading on the pile cap and/or on a debris raft lodged against the bent - upstream pile failure as a beam-column due to a combined P-load and a lateral flood water loading on a debris raft forming at an elevation of 7.5 ft below the top of the bent cap. ? The refined/2nd edition ?ST? is an improvement of the original ?ST? (Phase II ?ST?) in three important areas, i.e., - it has an expanded scope of applicability, checks for other possible failures, works with more realistic loadings, and includes other refinements as reported herein - it refers the user to 2nd tiers of screening for those bents not successfully passing the 1st tier of screening of the original ?ST? - it has a computer version available for use. 200 ? Perform an overview reading of this report to develop an understanding of the workings of the ?ST? and the refinements and changes that were made in developing this refined/2nd edition ?ST? from the original Phase II ?ST?. ? Perform a close reading of Chapter 2 to assist in accomplishing the above bullet. ? Perform a close reading of Chapter 4 and the flowcharts therein to gain a detailed understanding of the changes and refinements included in the refined/2nd edition ?ST? and the 2nd Tier Screenings included in the refined ?ST?. ? Manually work through at least some of the example application cases given in Chapter 5. ? Closely read this last Conclusion and Recommendation Chapter which summarizes the major changes and refinements made in the ?ST?. ? Read Part II of the Project Final Report to understand the automated version of the refined ?ST?. ? Work through some of the example application cases in the Part II Report to develop a working knowledge of the automated refined ?ST?. 201 REFERENCES Ramey, G.E., and D.A. Brown, ?Stability of Highway Bridges Subject to Scour - Phase I,? Alabama Department of Transportation Project 930-585, Final Report, September 2004. GTSTRUDL Reference Manual, Vol. 3, February 2002. Ramey, G.E., Brown, D.A., et. al., ?Stability of Highway Bridges Subject to Scour - Phase II,? Alabama Department of Transportation Project 930-608, Final Report, January 2006. Ramey, G.E., Brown, D.A., et.al., ?Screening Tool to Assess Adequacy of Bridge Pile Bents for Extreme Flood/Scour Events,? Alabama Department of Transportation Project 930-608 Report, January 2006. Ramey, G.E., Brown, D.A., et.al., ?Stability of Highway Bridges Subject to Scour - Phase II: Screening Tool Users Guide,? Alabama Department of Transportation Project 930-608 Report, January 2006. 202 Hughes, D. and Ramey, G.E., ?Stability of Highway Bridges Subject to Scour - Phase II - Part II: Bridge Bent P-Delta Curves in Transverse Direction Using FB-Pier and GTSTRUDL Pushover Analysis Procedures?, Alabama Department of Transportation Project 930-608 Interim Report, June 2005. 203 APPENDIX A: EXAMPLE GTSTRUDL INPUT CODE FOR PUSHOVER ANALYSIS FOR VARIOUS BENT CONFIGURATIONS 204 Example 1: 3-Pile Bent, Unbraced, Symmetric Load and Scour STRUDL ' ' $$ $$ This GTSTRUDL file created from GTMenu on 3/ 7/2007 $$ UNITS INCH KIPS DEG FAH JOINT COORDINATES GLOBAL 1 0 0 2 109.5 0 3 219 0 4 13.5 108 5 109.5 108 6 205.5 108 TYPE PLANE FRAME MEMBER INCIDENCES 1 1 4 2 2 5 3 3 6 4 4 5 5 5 6 UNITS INCH KIPS DEG FAH MEMBER PROPERTIES TABLE 'M/S/HP9 ' 'HP10x42 ' 1 2 3 MEMBER PROPERTIES PRISMATIC AX 8.6400000E+02 IX 1.0000000E+07 - IY 1.0000000E+07 IZ 4.1472000E+04 4 5 STATUS SUPPORT - 1 2 3 UNITS INCH KIPS DEG FAH JOINT RELEASES 1 2 3 - MOM Z UNITS INCH KIPS DEG FAH CONSTANTS BETA 9.0000000E+01 - 1 2 3 MATERIAL STEEL MATERIAL CONCRETE - 4 5 UNITS INCH KIPS DEG FAH LOADING 'CONST' JOINT LOADS FOR Y -6.0000001E+01 4 5 6 UNITS INCH KIPS DEG FAH LOADING 'INCR' JOINT LOADS FOR X 1.0000000E+00 4 NONLINEAR EFFECTS GEOMETRY ALL MEMBERS PLASTIC HINGE - 205 FIBER GEOMETRY NTF 1 NTW 1 NBF 8 ND 8 LH 3.0 - STEEL FY 36.0 ESH .124 ESU .2 FSU 36.001 ALPHA 0.0 MEMBER 1 2 3 LOAD LIST ALL PUSHOVER ANALYSIS DATA CONSTANT LOAD 'CONST' INCREMENTAL LOAD 'INCR' MAXIMUM NUMBER OF LOAD INCREMENTS 50 MAXIMUM NUMBER OF TRIALS 20 LOADING RATE 1.000000 CONVERGENCE RATE 0.500000 CONVERGENCE TOLERENCE COLLAPSE 0.000100 CONVERGENCE TOLERANCE DISPLACEMENT 0.001000 MAXIMUM NUMBER OF CYCLES 50 DISPLACEMENT CONTROL OFF END PERFORM PUSHOVER ANALYSIS 206 Example 2: 4-Pile Bent, Braced, Unsymmetric Load, Symmetric Scour STRUDL ' ' $$ $$ This GTSTRUDL file created from GTMenu on 3/20/2007 $$ UNITS INCH KIPS DEG FAH JOINT COORDINATES GLOBAL 1 -22.5 -180 2 120 -180 3 216 -180 4 358.5 -180 5 24 196 6 120 196 7 216 196 8 312 196 9 5.25 42 10 330.75 42 11 21.75 174 12 314.25 174 13 120 90.0857142857 14 216 90.0857142857 15 120 130.314285714 16 216 130.314285714 TYPE SPACE FRAME MEMBER INCIDENCES 1 5 6 2 6 7 3 7 8 4 1 9 5 9 11 6 11 5 7 2 13 8 13 15 9 15 6 10 3 14 11 14 16 12 16 7 13 4 10 14 10 12 15 12 8 16 11 15 17 15 14 18 14 10 19 9 13 20 13 16 21 16 12 UNITS INCH KIPS DEG FAH MEMBER PROPERTIES PRISMATIC AX 864 IX 1000000 IY 1000000 IZ 41472 1 2 3 MEMBER PROPERTIES TABLE 'M/S/HP9 ' 'HP12x53 ' 4 5 6 7 8 9 10 11 12 13 14 15 MEMBER PROPERTIES TABLE 'CHANNEL9 ' 'C4x7.25 ' 16 17 18 19 20 21 STATUS SUPPORT - 207 1 2 3 4 5 6 7 8 UNITS INCH KIPS DEG FAH JOINT RELEASES 1 2 3 4 MOM X Y Z 5 6 7 8 FOR X Y MOM Z UNITS INCH KIPS DEG FAH CONSTANTS BETA 90 - 4 5 6 7 8 9 10 11 12 13 14 15 MEMBER RELEASES 16 17 18 19 20 21 START MOM Y Z END MOM Y Z MATERIAL STEEL MATERIAL CONCRETE 1 2 3 UNITS INCH KIPS DEG FAH LOADING 'CONST' JOINT LOADS FOR Y -80 5 6 JOINT LOADS FOR Y -53 7 8 UNITS INCH KIPS DEG FAH LOADING 'INCR' JOINT LOADS FOR X 1 5 NONLINEAR EFFECTS GEOMETRY ALL MEMBERS PLASTIC HINGE - FIBER GEOMETRY NTF 1 NTW 1 NBF 8 ND 8 LH 3.0 - STEEL FY 36.0 ESH .124 ESU .2 FSU 36.001 ALPHA 0.0 - MEMBER 4 5 6 7 8 9 10 11 12 13 14 15 PLASTIC HINGE - FIBER GEOMETRY NTF 1 NTW 1 NBF 8 ND 8 LH 3.0 - STEEL FY 16.1 ESH .124 ESU .2 FSU 16.101 ALPHA 0.0 - MEMBER 16 17 18 LOAD LIST ALL PUSHOVER ANALYSIS DATA CONSTANT LOAD 'CONST' INCREMENTAL LOAD 'INCR' MAXIMUM NUMBER OF LOAD INCREMENTS 100 MAXIMUM NUMBER OF TRIALS 20 LOADING RATE 1.000000 CONVERGENCE RATE 0.500000 CONVERGENCE TOLERENCE COLLAPSE 0.000100 CONVERGENCE TOLERANCE DISPLACEMENT 0.001000 MAXIMUM NUMBER OF CYCLES 50 DISPLACEMENT CONTROL OFF END PERFORM PUSHOVER ANALYSIS 208 Example 3: 5-Pile Bent, 2-Story, Braced, Symmetric Load, Unsym. Scour STRUDL ' ' $$ $$ This GTSTRUDL file created on 1/ 25/2008 $$ UNITS INCH KIPS DEG FAH JOINT COORDINATES GLOBAL 1 -7.5 -60 S 2 126 -48 S 3 222 -40 S 4 318 -30 S 5 446.5 -20 S 6 30 240 S 7 126 240 S 8 222 240 S 9 318 240 S 10 414 240 S 11 5.25 42 12 15.75 126 13 16.5 132 14 17.25 138 15 27.75 222 16 126 65.9787234043 17 126 104.106382979 18 126 132 19 126 160.894736842 20 126 201.315789474 21 222 85.0425531915 22 222 132 23 222 181.105263158 24 318 65.9787234043 25 318 104.106382979 26 318 132 27 318 160.894736842 28 318 201.315789474 29 438.75 42 30 428.25 126 31 427.5 132 32 426.75 138 33 416.25 222 TYPE SPACE FRAME MEMBER INCIDENCES 1 6 7 2 7 8 3 8 9 4 9 10 5 1 11 6 11 12 7 12 13 8 13 14 9 14 15 10 15 6 11 2 16 12 16 17 13 17 18 14 18 19 15 19 20 209 16 20 7 17 3 21 18 21 22 19 22 23 20 23 8 21 4 24 22 24 25 23 25 26 24 26 27 25 27 28 26 28 9 27 5 29 28 29 30 29 30 31 30 31 32 31 32 33 32 33 10 33 15 20 34 20 23 35 23 27 36 27 32 37 12 17 38 17 21 39 21 24 40 24 29 41 14 19 42 19 23 43 23 28 44 28 33 45 11 16 46 16 21 47 21 25 48 25 30 49 13 18 50 18 22 51 22 26 52 26 31 UNITS INCH KIPS DEG FAH MEMBER PROPERTIES TABLE 'M/S/HP9 ' 'HP10x42 ' 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 MEMBER PROPERTIES TABLE 'CHANNEL9 ' 'C4x7.25 ' 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 MEMBER PROPERTIES PRISMATIC AX 864 IX 1000000 IY 1000000 IZ 41472 1 2 3 4 UNITS INCH KIPS DEG FAH JOINT RELEASES 1 2 3 4 5 MOM X Y Z 6 7 8 9 10 FOR X Y MOM Z UNITS INCH KIPS DEG FAH CONSTANTS BETA 90 - 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 MEMBER RELEASES 210 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 START MOM Y Z END MOM Y Z MATERIAL STEEL MATERIAL CONCRETE 1 2 3 4 UNITS INCH KIPS DEG FAH LOADING 'CONST' JOINT LOADS FOR Y -80 6 7 8 9 10 UNITS INCH KIPS DEG FAH LOADING 'INCR' JOINT LOADS FOR X 1 6 NONLINEAR EFFECTS GEOMETRY ALL MEMBERS PLASTIC HINGE - FIBER GEOMETRY NTF 1 NTW 1 NBF 8 ND 8 LH 3.0 - STEEL FY 36.0 ESH .124 ESU .2 FSU 36.001 ALPHA 0.0 - MEMBER 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 PLASTIC HINGE - FIBER GEOMETRY NTF 1 NTW 1 NBF 8 ND 8 LH 3.0 - STEEL FY 16.1 ESH .124 ESU .2 FSU 16.101 ALPHA 0.0 - MEMBER 33 34 35 36 37 38 39 40 LOAD LIST ALL PUSHOVER ANALYSIS DATA CONSTANT LOAD 'CONST' INCREMENTAL LOAD 'INCR' MAXIMUM NUMBER OF LOAD INCREMENTS 100 MAXIMUM NUMBER OF TRIALS 20 LOADING RATE 1.000000 CONVERGENCE RATE 0.500000 CONVERGENCE TOLERENCE COLLAPSE 0.000100 CONVERGENCE TOLERANCE DISPLACEMENT 0.001000 MAXIMUM NUMBER OF CYCLES 50 DISPLACEMENT CONTROL OFF END PERFORM PUSHOVER ANALYSIS 211 Example 4: 6-Pile Bent, Double X-Braced, Symmetric Load and Scour STRUDL ' ' $$ $$ This GTSTRUDL file created on 1/ 25/2008 $$ UNITS INCH KIPS DEG FAH JOINT COORDINATES GLOBAL 1 -37.5 -300 S 2 120 -300 S 3 216 -300 S 4 312 -300 S 5 408 -300 S 6 565.5 -300 S 7 24 192 S 8 120 192 S 9 216 192 S 10 312 192 S 11 408 192 S 12 504 192 S 13 5.25 42 14 21.75 174 15 120 91.3789731051 16 120 129.317829457 17 216 42 18 216 85.6589147287 19 216 132.689486553 20 216 174 21 312 42 22 312 85.6589147287 23 312 132.689486553 24 312 174 25 408 91.3789731051 26 408 129.317829457 27 522.75 42 28 506.25 174 TYPE SPACE FRAME MEMBER INCIDENCES 1 7 8 2 8 9 3 9 10 4 10 11 5 11 12 6 1 13 7 13 14 8 14 7 9 2 15 10 15 16 11 16 8 12 3 17 13 17 18 14 18 19 15 19 20 16 20 9 17 4 21 18 21 22 19 22 23 20 23 24 212 21 24 10 22 5 25 23 25 26 24 26 11 25 6 27 26 27 28 27 28 12 28 14 16 29 16 18 30 18 21 31 20 23 32 23 25 33 25 27 34 13 15 35 15 19 36 19 24 37 17 22 38 22 26 39 26 28 UNITS INCH KIPS DEG FAH MEMBER PROPERTIES TABLE 'M/S/HP9 ' 'HP12x53 ' 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 MEMBER PROPERTIES TABLE 'CHANNEL9 ' 'C4x7.25 ' 28 29 30 31 32 33 34 35 36 37 38 39 MEMBER PROPERTIES PRISMATIC AX 864 IX 10000000 IY 10000000 IZ 41472 1 2 3 4 5 UNITS INCH KIPS DEG FAH JOINT RELEASES 1 2 3 4 5 6 MOM X Y Z 7 8 9 10 11 12 FOR X Y MOM Z UNITS INCH KIPS DEG FAH CONSTANTS BETA 90 - 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 MEMBER RELEASES 28 29 30 31 32 33 34 35 36 37 38 39 START MOM Y Z END MOM Y Z MATERIAL STEEL MATERIAL CONCRETE 1 2 3 4 5 UNITS INCH KIPS DEG FAH LOADING 'CONST' JOINT LOADS FOR Y -80 7 8 9 10 11 12 UNITS INCH KIPS DEG FAH LOADING 'INCR' JOINT LOADS FOR X 1 7 NONLINEAR EFFECTS GEOMETRY ALL MEMBERS PLASTIC HINGE - 213 FIBER GEOMETRY NTF 1 NTW 1 NBF 8 ND 8 LH 3.0 - STEEL FY 36.0 ESH .124 ESU .2 FSU 36.001 ALPHA 0.0 - MEMBER 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 PLASTIC HINGE - FIBER GEOMETRY NTF 1 NTW 1 NBF 8 ND 8 LH 3.0 - STEEL FY 16.1 ESH .124 ESU .2 FSU 16.101 ALPHA 0.0 - MEMBER 28 29 30 31 32 33 LOAD LIST ALL PUSHOVER ANALYSIS DATA CONSTANT LOAD 'CONST' INCREMENTAL LOAD 'INCR' MAXIMUM NUMBER OF LOAD INCREMENTS 100 MAXIMUM NUMBER OF TRIALS 20 LOADING RATE 1.000000 CONVERGENCE RATE 0.500000 CONVERGENCE TOLERENCE COLLAPSE 0.000100 CONVERGENCE TOLERANCE DISPLACEMENT 0.001000 MAXIMUM NUMBER OF CYCLES 50 DISPLACEMENT CONTROL OFF END PERFORM PUSHOVER ANALYSIS