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 Xbraced 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 bentsupported 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 Tier2 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 CONTINUOUSSPAN
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 ContinuousSpan Superstructures on Bridge/Bent Pushover ....15
Effect of ContinuousSpan Superstructures on Bent Pile Buckling ..........21
Pushover Loads for Additional Pload and Scour Levels .........................24
Pushover Loads for Unsymmetric Pload Distribution..............................51
Pushover Loads for Variable Scour Distribution.......................................65
ix
Pushover Loads for Unsymmetric Pload and Variable Scour
Distributions ..................................................................................86
Bent Pushover Failure in Terms of Critical Scour Level...........................95
Check Upstream Bent Pile for BeamColumn Failure from Debris Raft
Loading.......................................................................................104
Effect of Height of Debris Raft Loading on Bent Pushover ....................117
Additional Expansions of Applicability of the Tier1 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 TIER2 SCREENINGS..............................140
General ..................................................................................................140
Refined/2nd Edition ?ST?.........................................................................141
Second Tier/Tier2 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 TIER2 ?ST?.....................161
x
General ..................................................................................................161
Bent/Site Conditions to Check For Need/Applicability of the ?ST?..........162
Example Applications for Tier2 Pile Plunging Failure Check ................163
Example Applications for Tier2 Buckling Failure Check........................173
Example Applications for Tier2 Bent Pushover Failure Check..............177
Example Application for Bent Upstream Pile BeamColumn Failure
Check..........................................................................................188
Closure ..................................................................................................190
CHAPTER 6: CONCLUSIONS AND RECOMMENDATIONS ..........................191
General ..................................................................................................191
Conclusions ...........................................................................................192
Additional Pile Axial Pload 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 Pload Levels.........................194
Pushover Loads for Unsymmetric Pload 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 BeamColumn .....................................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 3Pile and 4Pile 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 3Pile and 4Pile Bridge Bents with
HP10X42 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4
for Varying Values of PLoad and ?H+S?...................................................29
Table 2.3b. Pushover Load, Ft, for Unbraced 3Pile and 4Pile Bridge Bents with
HP12X53 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4
for Varying Values of PLoad and ?H+S?...................................................30
Table 2.4a. Pushover Load, Ft, for Unbraced 5Pile and 6Pile Bridge Bents with
HP10X42 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4
for Varying Values of PLoad and ?H+S?...................................................31
Table 2.4b. Pushover Load, Ft, for Unbraced 5Pile and 6Pile Bridge Bents with
HP12X53 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4
for Symmetric Distribution of Varying Values of PLoad and ?H+S?..........32
xiii
Table 2.5a. Pushover Load, Ft, for XBraced 3Pile and 4Pile Bridge Bents with
HP10X42 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4
for Symmetric Distribution of Varying Values of PLoad and ?H+S?..........33
Table 2.5b. Pushover Load, Ft, for XBraced 3Pile and 4Pile Bridge Bents with
HP12X53 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4
for Symmetric Distribution of Varying Values of PLoad and ?H+S?..........34
Table 2.6a. Pushover Load, Ft, for Single Story XBraced 5Pile and 6Pile
Bridge Bents with HP10X42 Piles and Reinforced Concrete Bent Cap with
Igross = 41,470 in4 for Symmetric Distribution of Varying Values of PLoad
and ?H+S? .................................................................................................35
Table 2.6b. Pushover Load, Ft, for Single Story XBraced 5Pile and 6Pile
Bridge Bents with HP12X53 Piles and Reinforced Concrete Bent Cap with
Igross = 41,470 in4 for Symmetric Distribution of Varying Values of PLoad
and ?H+S? .................................................................................................36
Table 2.7a. Pushover Load, Ft, for 2 Story XBraced 3Pile and 4Pile Bridge
Bents with HP10X42 Piles and Reinforced Concrete Bent Cap with Igross =
41,470 in4 for Symmetric Distribution of Varying Values of PLoad and
?H+S? ........................................................................................................45
Table 2.7b. Pushover Load, Ft, for 2 Story XBraced 3Pile and 4Pile Bridge
Bents with HP12X53 Piles and Reinforced Concrete Bent Cap with Igross =
41,470 in4 for Symmetric Distribution of Varying Values of PLoad and
?H+S? ........................................................................................................46
xiv
Table 2.8a. Pushover Load, Ft, for 2 Story XBraced 5Pile and 6Pile Bridge
Bents with HP10X42 Piles and Reinforced Concrete Bent Cap with Igross =
41,470 in4 for Symmetric Distribution of Varying Values of PLoad and
?H+S? ........................................................................................................47
Table 2.8b. Pushover Load, Ft, for 2 Story XBraced 5Pile and 6Pile Bridge
Bents with HP12X53 Piles and Reinforced Concrete Bent Cap with Igross =
41,470 in4 for Symmetric Distribution of Varying Values of PLoad and
?H+S? ........................................................................................................48
Table 2.9a. Pushover Load, Ft, for Double XBraced 1Story and 2Story 6Pile
Bridge Bents with HP10X42 Piles and Concrete Cap with Igross = 41,470 in4
for Symmetric PLoads and Scour ...........................................................49
Table 2.9b. Pushover Load, Ft, for Double XBraced 1Story and 2Story 6Pile
Bridge Bents with HP12X53 Piles and Concrete Cap with Igross = 41,470 in4
for Symmetric PLoads and Scour ...........................................................50
Table 2.10a. Pushover Load, Ft, for Unbraced 3Pile and 4Pile Bridge Bents
with HP10X42 Piles and Concrete Cap with Igross = 41,470 in4 for
Unsymmetric PLoadings and Varying Values of ?H+S? ...........................55
Table 2.10b. Pushover Load, Ft, for Unbraced 3Pile and 4Pile Bridge Bents
with HP12X53 Piles and Concrete Cap with Igross = 41,470 in4 for
Unsymmetric PLoadings and Varying Values of ?H+S? ...........................56
Table 2.11a. Pushover Load, Ft, for Single Story XBraced 3Pile and 4Pile
Bridge Bents with HP10X42 Piles and Concrete Cap with Igross = 41,470 in4
for Unsymmetric PLoadings and Varying Values of ?H+S? ......................57
xv
Table 2.11b. Pushover Load, Ft, for Single Story XBraced 3Pile and 4Pile
Bridge Bents with HP12X53 Piles and Concrete Cap with Igross = 41,470 in4
for Unsymmetric PLoadings and Varying Values of ?H+S? ......................58
Table 2.12a. Pushover Load, Ft, for 2Story XBraced 3Pile and 4Pile Bridge
Bents with HP10X42 Piles and Concrete Cap with Igross = 41,470 in4 for
Varying Values of ?H+S? and Unsymmetric PLoadings ...........................63
Table 2.12b. Pushover Load, Ft, for 2Story XBraced 3Pile and 4Pile Bridge
Bents with HP12X53 Piles and Concrete Cap with Igross = 41,470 in4 for
Varying Values of ?H+S? and Unsymmetric PLoadings ...........................64
Table 2.13a. Pushover Load, Ft, for Unbraced 3Pile and 4Pile Bridge Bents
with HP10X42 Piles and Reinforced Concrete Bent Cap with Igross = 41,470
in4 for Varying Values of PLoad and for Variable Scour and ?H+S?
Distributions .............................................................................................70
Table 2.13b. Pushover Load, Ft, for Unbraced 3Pile and 4Pile Bridge Bents
with HP12X53 Piles and Reinforced Concrete Bent Cap with Igross = 41,470
in4 for Varying Values of PLoad and for Variable Scour and ?H+S?
Distributions .............................................................................................71
Table 2.14a. Pushover Load, Ft, for Unbraced 5Pile and 6Pile Bridge Bents
with HP10X42 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric
PLoads and Variable Scour and ?H+S? Distributions...............................72
Table 2.14b. Pushover Load, Ft, for Unbraced 5Pile and 6Pile Bridge Bents
with HP12X53 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric
PLoads and Variable Scour and ?H+S? Distributions...............................73
xvi
Table 2.15a. Pushover Load, Ft, for Single Story XBraced 3Pile and 4Pile
Bridge Bents with HP10X42 Piles and Reinforced Concrete Bent Cap with
Igross = 41,470 in4 for Symmetric Distribution of Varying Values of PLoad
and ?H+S? for Variable Scour Distribution.................................................74
Table 2.15b. Pushover Load, Ft, for Single Story XBraced 3Pile and 4Pile
Bridge Bents with HP12X53 Piles and Reinforced Concrete Bent Cap with
Igross = 41,470 in4 for Varying Values of PLoad and for Variable Scour and
?H+S? Distributions....................................................................................75
Table 2.16a. Pushover Load, Ft, for Single Story XBraced 5Pile and 6Pile
Bridge Bents with HP10X42 Piles and Concrete Cap with Igross = 41,470 in4
for Symmetric PLoads and Variable Scour and ?H+S? Distributions........76
Table 2.16b. Pushover Load, Ft, for Single Story XBraced 5Pile and 6Pile
Bridge Bents with HP12X53 Piles and Concrete Cap with Igross = 41,470 in4
for Symmetric PLoads and Variable Scour and ?H+S? Distributions........77
Table 2.17a. Pushover Load, Ft, for 2Story XBraced 3Pile and 4Pile Bridge
Bents with HP10X42 Piles and Concrete Cap with Igross = 41,470 in4 for
Symmetric PLoadings and Variable Scour and ?H+S? Distributions ........80
Table 2.17b. Pushover Load, Ft, for 2Story XBraced 3Pile and 4Pile Bridge
Bents with HP12X53 Piles and Concrete Cap with Igross = 41,470 in4 for
Symmetric PLoadings and Variable Scour and ?H+S? Distributions ........81
Table 2.18a. Pushover Load, Ft, for 2Story XBraced 5Pile and 6Pile Bridge
Bents with HP10X42 Piles and Concrete Cap with Igross = 41,470 in4 for
Symmetric PLoads and Variable Scour and ?H+S? Distributions .............82
xvii
Table 2.18b. Pushover Load, Ft, for 2Story XBraced 5Pile and 6Pile Bridge
Bents with HP12X53 Piles and Concrete Cap with Igross = 41,470 in4 for
Symmetric PLoads and Variable Scour and ?H+S? Distributions .............83
Table 2.19a. Pushover Load, Ft, for Double XBraced 1Story and 2Story 6Pile
Bridge Bents with HP10X42 Piles and Concrete Cap with Igross = 41,470 in4
for Symmetric PLoads and Variable Scour and ?H+S? Distributions........84
Table 2.19b. Pushover Load, Ft, for Double XBraced 1Story and 2Story 6Pile
Bridge Bents with HP12X53 Piles and Concrete Cap with Igross = 41,470 in4
for Symmetric PLoads and Variable Scour and ?H+S? Distributions........85
Table 2.20a. Pushover Load, Ft, for Unbraced 3Pile and 4Pile Bridge Bents
with HP10X42 Piles and Concrete Cap with Igross = 41,470 in4 for
Unsymmetric PLoadings and Variable Scour and ?H+S? Distributions ....88
Table 2.20b. Pushover Load, Ft, for Unbraced 3Pile and 4Pile Bridge Bents
with HP12X53 Piles and Concrete Cap with Igross = 41,470 in4 for
Unsymmetric PLoadings and Variable Scour and ?H+S? Distributions ....89
Table 2.21a. Pushover Load, Ft, for Single Story XBraced 3Pile and 4Pile
Bridge Bents with HP10X42 Piles and Concrete Cap with Igross = 41,470 in4
for Unsymmetric PLoadings and for Variable Scour and ?H+S?
Distributions .............................................................................................90
Table 2.21b. Pushover Load, Ft, for Single Story XBraced 3Pile and 4Pile
Bridge Bents with HP12X53 Piles and Concrete Cap with Igross = 41,470 in4
for Unsymmetric PLoadings and for Variable Scour and ?H+S?
Distributions .............................................................................................91
xviii
Table 2.22a. Pushover Load, Ft, for 2 Story XBraced 3Pile and 4Pile Bridge
Bents with HP10X42 Piles and Concrete Cap with Igross = 41,470 in4 for
Unsymmetric PLoadings and for Variable Scour and ?H+S?
Distributions .............................................................................................93
Table 2.22b. Pushover Load, Ft, for 2 Story XBraced 3Pile and 4Pile Bridge
Bents with HP12X53 Piles and Concrete Cap with Igross = 41,470 in4 for
Unsymmetric PLoadings and for Variable Scour and ?H+S?
Distributions .............................................................................................94
Table 2.23a. Critical Uniform Scour, SCR, of HP10X42 3, 4, 5, 6Pile Bents without
XBracing 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, 6Pile Bents without
XBracing 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, 6Pile Bents with
XBracing 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, 6Pile Bents with
XBracing 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, 6Pile Bents
without XBracing 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, 6Pile Bents
without XBracing 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, 6Pile Bents with
XBracing 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, 6Pile Bents with
XBracing to Resist Ft max design = 12.15k (includes a FS = 1.25) .............103
Table 2.27. Upstream Pile BeamColumn 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 XBraced 3
Pile and 4Pile Bridge Bents of Height H = 21 ft with HP10X42 Piles and
Concrete Bent Cap with Igross = 41,470 in4 for Symmetric PLoads and
Uniform Scour........................................................................................120
Table 2.29. Pushover Load, Ft, at Low Position for 2Story XBraced 3Pile 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 4Pile Bents
(HP10X42 Piles) and P = 100k ......................................................................9
Fig. 2.3. Stiffness and Relative Stiffness Parameters for Typical 3Pile Bent ....11
Fig. 2.4. XBraced Bent Qualitative Lateral LoadDeformation 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 XBraced
Pile Bents (from Phase II Research)........................................................18
Fig. 2.9. 2Span SS Bridge ................................................................................19
Fig. 2.10. MultiSpanBridge with Many Rigid SS Spans.....................................19
Fig. 2.11. MultiSpan Bridge Composed of 2Span Continuous Segments........19
Fig. 2.12. Maximum Bent Forces for Continuous Span Bridges.........................20
Fig. 2.13. FBent Max on 2Span 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 4Pile
Bents (HP10X42 Piles) with PLoads of 60k, 80k, 100k, 120k, 140k, and
160k..........................................................................................................37
Fig. 2.16. Pushover Load vs. Bent Height Plus Scour for Unbraced 3 and 4Pile
Bents (HP12X53 Piles) with PLoads of 60k, 80k, 100k, 120k, 140k, and
160k..........................................................................................................38
Fig. 2.17. Pushover Load vs. Bent Height Plus Scour for Single Story XBraced
3 and 4Pile Bents (HP10X42 Piles) with PLoads of 60k and 160k............39
Fig. 2.18. Pushover Load vs. Bent Height Plus Scour for Single Story XBraced
3 and 4Pile Bents (HP12X53 Piles) with PLoads of 60k and 160k............40
Fig. 2.19a. GTSTRUDL Pushover Analysis Results for 13 ft Tall Non XBraced
HP10X42 Pile Bents Subject to Scour.........................................................41
Fig. 2.19b. GTSTRUDL Pushover Analysis Results for 13 ft Tall Non XBraced
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 6,5,4,3Piles of HP10X42 and P = 100k.....................43
Fig. 2.21. Pushover Force vs. Scour (H+S) for 5Pile Bent with H=10?, HP10X42,
and P = 60k ..............................................................................................44
Fig. 2.22. 3Pile Bent Pload Distributions..........................................................52
Fig. 2.23. 4Pile Bent Pload Distributions..........................................................52
Fig. 2.24. Symmetric and Nonsymmetric Pload Distributions ...........................53
xxii
Fig. 2.25. Unsymmetric Pload Levels and Distributions Used in Phase III
Work ........................................................................................................53
Fig. 2.26. Pushover Load vs. Bent Height Plus Scour for Unbraced 3 and 4Pile
Bents (HP10X42 Piles) with Sym. and Unsym. PLoads.............................59
Fig. 2.27. Pushover Load vs. Bent Height Plus Scour for Unbraced 3 and 4Pile
Bents (HP12X53 Piles) with Sym. and Unsym. PLoads.............................60
Fig. 2.28. Pushover Load vs. Bent Height Plus Scour for Single Story XBraced
3 and 4Pile Bents (HP10X42 Piles) with Sym. and Unsym. PLoads........61
Fig. 2.29. Pushover Load vs. Bent Height Plus Scour for Single Story XBraced
3 and 4Pile Bents (HP12X53 Piles) with Sym. and Unsym. PLoads........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 4Pile
Bents (HP10X42 Piles) with Uniform and Variable Scour............................78
Fig. 2.34. Pushover Load vs. Bent Height Plus Scour for XBraced 3 and 4Pile
Bents (HP10X42 Piles) with Uniform and Variable Scour............................79
Fig. 2.35. Pushover Load vs. Bent Height Plus Scour for Unbraced and X
Braced 3Pile Bents (HP10X42 Piles) with Uniform PLoad and Scour and
with Unsym. PLoad 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 PinnedEnd Condition..............106
Fig. 2.38. Upstream Pile, P1, Mmax Values for FixedEnd Condition ................107
Fig. 2.39. XBraced Bent with FtLoad at Level of Horizontal Brace.................108
Fig. 2.40. Checking Upstream Pile of Maximum Height Unbraced Bent as a
BeamColumn........................................................................................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 BeamColumn......116
Fig. 2.43. TwoStory XBraced 3Pile 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, 1Story XBraced, and 2Story XBraced Bent
Deformations..........................................................................................121
Fig. 2.45. GTSTRUDL Generated Deformations of 3Pile Bent from Ft
Loadings ................................................................................................122
Fig. 2.46. GTSTRUDL Generated Deformations of 4Pile 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, 4Pile 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 PLoading for 4Pile Bents............................................136
Fig. 3.8. 34? Span SS Bridge with 7? Deck, AASHTO Type II Girders (3 Girders
at 8? Spacing), Jersey Barriers, 3Pile 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 PLoading for 3Pile 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 KickOut and Plunging Evaluation Module................145
Fig. 4.4. Enlargement of Refined Buckling Evaluation Module.........................147
Fig. 4.5a. Typical ALDOT XBraced Pile Bent Geometry.................................148
Fig. 4.5b. Transverse Buckling Modes and Equations for XBraced Bents......149
Fig. 4.6. Enlargement of the Bent Pushover Evaluation Module ......................150
Fig. 4.7. Enlargement of Upstream Pile BeamColumn Evaluation Module .....152
Fig. 4.8a. Tier2/2A Screening for Pile Plunging Adequacy Assessment.........155
Fig. 4.8b. Tier2/2B Screening for Pile Plunging Adequacy Assessment.........156
Fig. 4.9a. Tier2/4A Screening for Bent Pushover Adequacy Assessment ......158
Fig. 4.9b. Tier2/4B Screening for Bent Pushover Adequacy Assessment ......159
xxv
Fig. 5.1. Example Problem 1 for KickOut and Plunging ..................................164
Fig. 5.2. Example Problem 1 for KickOut and Plunging (Continued)...............165
Fig. 5.3. Example Problem 1 for KickOut 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 BeamColumn...........................................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 Tier2 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 userfriendly 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, followup assessment procedures for those
bents that do not pass through the ?screening tool? with an evaluation
of ?the bent is safe from plunging (buckling, pushover)?. More
specifically, identify the appropriate followup checking procedures for
those bents where the ?screening tool? indicates that the ?bent should
be looked at more closely for possible plunging (buckling, pushover)
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 userfriendly 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 pushover 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 standalone 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 CONTINUOUSSPAN 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 5pile and 6pile bents as
well as 3pile and 4pile 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 castinplace 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 3pile and 4pile 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. 3Pile Bent
b. 4Pile Bent
8
Table 2.1. Ft for Unbraced 3Pile and 4Pile Bridge Bents for Varying
Values of Bent Cap Igross  HP10x42 Piles and P=100k
3Pile Bent 4Pile 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 4Pile Bents
(HP10x42 Piles) and P = 100k
10
It can be seen in Table 2.1 and Fig. 2.2 that for the 3pile bent, the
pushover load is essentially independent of the bent cap size/stiffness. For the
4pile 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 Xbraced bents (see Fig. 2.4) that the bracing
system maintains the relative geometrical integrity (with or without the HB1
brace shown in Fig. 2.4) of the bent in the region of the Xbracing and the bent
sidesways in the region below the Xbrace 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 3Pile Bent
Fig. 2.4. XBraced Bent Qualitative Lateral LoadDeformation 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 (3pile 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, 5pile
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 3pile bent. This additional axial load would
contribute to trying to ?plunge? or buckle the downstream pile; however, this pile
would get some ?leanon? 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 ContinuousSpan 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 3pile or 4pile 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 simplysupported 2span 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 multispan
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 2span bridge of Fig. 2.9.
Thus in this case, FB = Ft as it was for the 2SS span bridge of Fig. 2.9. This is
indicated in Fig. 2.10. For a multispan bridge composed of 2continuous 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. 2.82.11 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 4span 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
2Span Cont: FBent Max Applied = tF2 = 6.1k (Includes a F.S. = 1.25)
If PushoverCapacityF ? 6.1k the bent is OK for pushover
3Span 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
4Span 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
5Span 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 4Pile Bent with H=13?, P=120kips and A=6?
Pushover Analysis Results
b) HP10x42 XBraced 4Pile 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. 2Span SS Bridge
Fig. 2.10. MultiSpan Bridge with Many Rigid SS Spans
Fig. 2.11. MultiSpan Bridge Composed of 2Span Continuous Segments
20
a) SSSpans or 1Rigid Span Segments
b) 2Span Continuous Segments
c) 3Span Continuous Segments
Fig. 2.12. Maximum Bent Forces for Continuous Span Bridges
21
Fig. 2.13. FBent Max on 2Span Continuous Bridge when Ft is Applied at Bent
Where Superstructure has Continuity
2.5 Effect of ContinuousSpan 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 Xbraced 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 ContinuousSpan
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 Pload and Scour
In the Tier 1 Screening Tool, i.e., the Phase II work, possible pile/bent
failures via,
1. pile ?kickout?
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 ?kickout? 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 Ploads of
Bent
Max AppliedP
No. of Bent Piles .
Using levels of uniformly distributed Ploads (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 Pload 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
Pload 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 Ploads 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 Ploads somewhat less than
80k. Initially, in the new pushover analyses conducted for the Phase III work,
only the smaller 3pile and 4pile 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 5pile and 6pile bents analyses also be included, and this has
been done.
Results of additional pushover analyses for 3 and 4pile singlestory
bents for Ploads of 60k and 80k and scour of 25 ft have been added to those of
the earlier analyses for larger Ploads and lower scour levels and these are
shown in Tables 2.32.6. Also, these tables have been expanded to include 5
and 6pile bents. One can note in these tables that there is a very dramatic
reduction in pushover capacity after 5 ft of scour. For the 3pile 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 Pload levels.
27
To better illustrate the effect of the Pload level on a bent?s pushover
capacity, the data of Tables 2.32.6 are shown plotted on Pushover Force vs.
H+S curves in Figs. 2.152.18. Note in these tables and figures that bents with
the lower Ploads 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 5pile 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 5pile 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 Xbraced, they act primarily as
vertical trusses when subjected to Ft lateral loads prior to the occurrence of any
scour. However, after about 45 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 6pile bents that
are 2story and Xbraced for Ploads of 60k and 80k and scours of 25 ft have
been added to those generated in earlier analyses for larger Ploads 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 Ploaded bents have a significantly larger pushover
capacity than those with larger Ploads.
Lastly, additional pushover analyses for 1story and 2story 6pile bents
having double Xbracing across the width of the bent were performed for the
additional Ploads 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 3Pile and 4Pile Bridge Bents with
HP10x42 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4
for Varying Values of PLoad 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 3Pile and 4Pile Bridge Bents with
HP12x53 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4
for Varying Values of PLoad 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 5Pile and 6Pile Bridge Bents with
HP10x42 Piles and Reinforced Concrete Cap with Igross = 41,470 in4
of Varying Values of PLoad 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 5Pile Bridge Bents with HP12x53 Piles
and Reinforced Concrete Cap with Igross = 41,470 in4 for Symmetric Distribution
of Varying Values of PLoad 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 XBraced 3Pile and 4Pile Bridge Bents
with HP10x42 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4
for Symmetric Distribution of Varying Values of PLoad 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 XBraced 3Pile and 4Pile Bridge Bents
with HP12x53 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4
for Symmetric Distribution of Varying Values of PLoad 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 XBraced 5Pile and 6Pile Bridge
Bents with HP10x42 Piles and Reinforced Concrete Cap with Igross = 41,470 in4 for
Symmetric Distribution of Varying Values of PLoad 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 XBraced 5Pile and 6Pile Bridge
Bents with HP12x53 Piles and Reinforced Concrete Cap with Igross = 41,470 in4 for
Symmetric Distribution of Varying Values of PLoad 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
4Pile Bents (HP10x42 Piles) with PLoads of 60k, 80k, 100k, 120k, 140k, and
160k
38
Fig. 2.16. Pushover Load vs. Bent Height Plus Scour for Unbraced 3 and
4Pile Bents (HP12x53 Piles) with PLoads of 60k, 80k, 100k, 120k, 140k, and
160k
39
Fig. 2.17. Pushover Load vs. Bent Height Plus Scour for Single Story
XBraced 3 and 4Pile Bents (HP10x42 Piles) with PLoads of 60k and 160k
40
Fig. 2.18. Pushover Load vs. Bent Height Plus Scour for Single Story
XBraced 3 and 4Pile Bents (HP12x53 Piles) with PLoads of 60k and 160k
41
a) 3Pile Bent
b) 4Pile Bent
Fig. 2.19a. GTSTRUDL Pushover Analysis Results for 13 ft Tall Non X
Braced HP10x42 Pile Bents Subject to Scour
42
c) 5Pile Bent
d) 6Pile 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, 3Piles of HP10x42 and P=100k
44
Fig. 2.21. Pushover Force vs. Scour (H+S) for 5Pile 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 XBraced 3Pile and 4Pile Bridge Bents
with HP10x42 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4
for Symmetric Distribution of Varying Values of PLoad 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 XBraced 3Pile and 4Pile Bridge Bents
with HP12x53 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4
for Symmetric Distribution of Varying Values of PLoad 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 2Story XBraced 5Pile and 6Pile Bridge Bents
with HP10x42 Piles and Reinforced Concrete Cap with Igross = 41,470 in4 for
Symmetric Distribution of Varying Values of PLoad 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 2Story XBraced 5Pile and 6Pile Bridge Bents
with HP12x53 Piles and Reinforced Concrete Cap with Igross = 41,470 in4 for
Symmetric Distribution of Varying Values of PLoad 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 XBraced 1Story and 2Story 6Pile Bridge
Bents with HP10x42 Piles and Concrete Cap with Igross = 41,470 in4
for Symmetric PLoads 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
6Piles
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
6Piles
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 XBraced 1Story and 2Story 6Pile Bridge
Bents with HP12x53 Piles and Concrete Cap with Igross = 41,470 in4
for Symmetric PLoads 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
6Piles
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
6Piles
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 Pload Distribution
The Tier One Screening Tool (T1ST) assumes a uniform and symmetric
Pload 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 Pload 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 3pile and 4pile bents. Thus, for these bents, additional pushover
analyses were performed for the nonsymmetric Ploading shown in Fig. 2.25.
For 3pile and 4pile 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 Ploads for 3pile and 4pile
bents can be taken as shown in Fig. 2.25. These, then, are the distributions and
Pload values that were used in the pushover analyses of 3 and 4pile bents in
this Phase III work.
52
Fig. 2.22. 3Pile Bent Pload Distributions
Fig. 2.23. 4pile Bent Pload Distributions
53
Fig. 2.24. Symmetric and Nonsymmetric Pload Distributions
Fig. 2.25. Unsymmetric Pload Levels and Distributions Used in Phase III
Work
54
Results of the bent pushover analyses with unsymmetric Ploading,
resulting from applying LL only to the bridge upstream lane are presented in
Tables 2.10a and 2.10b for singlestory, unbraced, 3 and 4pile bents, and in
Tables 2.11a and 2.11b for singlestory, Xbraced, 3 and 4pile bents. Again, to
better illustrate the effect of Pload 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. 2.262.27, and for braced bents in Figs. 2.282.29. As can be
seen in all of these figures, the bent pushover load is a little smaller in every case
with the unsymmetric Pload distribution. This is due to the sidesway caused by
unsymmetric loading. Because the difference is so small, use of pushover
analysis having a symmetric Pload distribution was felt to be justifiable.
Results of bent pushover analyses with unsymmetric Ploadings on 2
story Xbraced 3 and 4pile 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 Pload
distribution. Again, because of the small difference, restricting pushover analysis
to those having a symmetric Pload distribution was felt to be justifiable.
Lastly, because of the small difference in pushover results for the
unsymmetric Pload distribution relative to that for the symmetric Pload
distribution, expansions of the pushover tables were not performed for S = 25ft
and for 5pile and 6pile bents.
55
Table 2.10a. Pushover Load, Ft, for Unbraced 3Pile and 4Pile Bridge Bents with
HP10x42 Piles and Concrete Cap with Igross = 41,470 in4
for Unsymmetric PLoadings 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 3Pile and 4Pile Bridge Bents with
HP12x53 Piles and Concrete Cap with Igross = 41,470 in4
for Unsymmetric PLoadings 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 XBraced 3Pile and 4Pile Bridge
Bents with HP10x42 Piles and Concrete Cap with Igross = 41,470 in4
for Unsymmetric PLoadings 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 XBraced 3Pile and 4Pile Bridge
Bents with HP12x53 Piles and Concrete Cap with Igross = 41,470 in4
for Unsymmetric PLoadings 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
4Pile Bents (HP10x42 Piles) with Sym. and Unsym. PLoads
60
Fig. 2.27. Pushover Load vs. Bent Height Plus Scour for Unbraced 3 and
4Pile Bents (HP12x53 Piles) with Sym. and Unsym. PLoads
61
Fig. 2.28. Pushover Load vs. Bent Height Plus Scour for Single Story
XBraced 3 and 4Pile Bents (HP10x42 Piles) with Sym. and Unsym. PLoads
62
Fig. 2.29. Pushover Load vs. Bent Height Plus Scour for Single Story
XBraced 3 and 4Pile Bents (HP12x53 Piles) with Sym. and Unsym. PLoads
63
Table 2.12a. Pushover Load, Ft, for 2Story XBraced 3Pile and 4Pile Bridge
Bents with HP10x42 Piles and Concrete Cap with Igross = 41,470 in4 for Varying
Values of ?H+S?and Unsymmetric PLoadings
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 2Story XBraced 3Pile and 4Pile Bridge
Bents with HP12x53 Piles and Concrete Cap with Igross = 41,470 in4 for Varying
Values of ?H+S?and Unsymmetric PLoadings
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 ?leanon? buckling support
and some ?leanon? 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 3pile bents and a few 4pile bents appear to be of concern
regarding possible pushover failures. Hence, we initially only modeled and
analyzed 3pile and 4pile 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 3pile 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
?leanon? 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 Xbraced 3, 4, 5, and 6pile 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 4pile 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 2.132.16 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 Xbraced bent
pushover load data vs. H+S in Tables 2.132.16, as shown in Figs. 2.33 and
2.34, respectively.
Results of bent pushover analyses for variable scour distributions for 2
story Xbraced 3, 4, 5 and 6pile bents with symmetric Pload 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 3Pile and 4Pile Bridge Bents with
HP10x42 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4
for Varying Values of PLoad 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 3Pile and 4Pile Bridge Bents with
HP12X53 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4
for Varying Values of PLoad 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 5Pile and 6Pile Bridge Bents with
HP10x42 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric PLoads
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 5Pile and 6Pile Bridge Bents with
HP12x53 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric PLoads
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 XBraced 3Pile and 4Pile Bridge
Bents with HP10x42 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4
for Symmetric Distribution of Varying Values of PLoad 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 XBraced 3Pile and 4Pile Bridge
Bents with HP12x53 Piles and Reinforced Concrete Bent Cap with Igross = 41,470 in4 for
Varying Values of PLoad 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 XBraced 5Pile and 6Pile Bridge
Bents with HP10x42 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric
PLoads 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 XBraced 5Pile and 6Pile Bridge
Bents with HP12x53 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric
PLoads 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 3Pile
and 4Pile Bents (HP10x42 Piles) with Uniform and Variable Scour
79
Fig. 2.34. Pushover Load vs. Bent Height Plus Scour for XBraced 3Pile
and 4Pile Bents (HP10x42 Piles) with Uniform and Variable Scour
80
Table 2.17a. Pushover Load, Ft, for 2Story XBraced 3Pile and 4Pile Bridge
Bents with HP10x42 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric
PLoadings 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 2Story XBraced 3Pile and 4Pile Bridge
Bents with HP12x53 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric
PLoadings 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 2Story XBraced 5Pile and 6Pile Bridge
Bents with HP10x42 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric
PLoads 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 2Story XBraced 5Pile and 6Pile Bridge
Bents with HP12x53 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric
PLoads 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 XBraced 1Story and 2Story 6Pile Bridge
Bents with HP10x42 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric
PLoads 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
6Piles
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
6Piles
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 XBraced 1Story and 2Story 6Pile Bridge
Bents with HP12x53 Piles and Concrete Cap with Igross = 41,470 in4 for Symmetric
PLoads 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
6Piles
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
6Piles
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 Pload 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 Pload and
nonuniform scour) would have the larger effect on a bent?s pushover capacity.
Pushover analyses of 3pile and 4pile bents were performed for a combination
of these conditions for a range of Ploads 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 4pile bents are adequate for
pushover, and almost all of the 3pile bents are adequate as well. This is not the
case for the HP10x42 pile bents. For these bents, almost all of the 4pile bents are
adequate, but most of the 3pile bents are not adequate for pushover. A subset
of the pushover loads of Tables 2.20a and 2.21a (for HP10x42 3pile bents) are
shown in Fig. 2.35 for convenience in comparing the effects of nonuniform Pload
and scour distributions versus uniform Pload and scour distributions on bent
pushover loads. As can be seen in that figure, for unbraced bents, the effect is
87
minimal; however, for Xbraced bents, the nonuniform Pload and scour
distributions yield significantly higher bent pushover capacities.
Results of pushover analyses for 2story Xbraced 3 and 4pile bents with
HP10x42 and HP12x53 piles for unsymmetric Ploads 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 Ploads and uniform scour in Tables 2.7 and 2.8 respectively, one can
see significantly larger pushover capacities for the nonuniform Pload and scour
situation. Thus, if one assumes uniform distributions of Ploads and scour, the
analyses results will be conservative.
88
Table 2.20a. Pushover Load, Ft, for Unbraced 3Pile and 4Pile Bridge Bents with
HP10x42 Piles and Concrete Cap with Igross = 41,470 in4 for Unsymmetric
PLoadings 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 3Pile and 4Pile Bridge Bents with
HP12x53 Piles and Concrete Cap with Igross = 41,470 in4 for Unsymmetric
PLoadings 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 XBraced 3Pile and 4Pile Bridge
Bents with HP10x42 Piles and Concrete Cap with Igross = 41,470 in4 for Unsymmetric
PLoadings 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 XBraced 3Pile and 4Pile Bridge
Bents with HP12x53 Piles and Concrete Cap with Igross = 41,470 in4 for Unsymmetric
PLoadings 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
XBraced 3Pile Bents (HP10x42 Piles) with Uniform PLoad and Scour and
with Unsym. PLoad and Variable Scour
93
Table 2.22a. Pushover Load, Ft, for 2 Story XBraced 3Pile and 4Pile Bridge
Bents with HP10X42 Piles and Concrete Cap with Igross = 41,470 in4 for Unsymmetric
PLoadings 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 XBraced 3Pile and 4Pile Bridge
Bents with HP12x53 Piles and Concrete Cap with Igross = 41,470 in4 for Unsymmetric
PLoadings 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 Ploads. These tables can in turn be used to determine SCR for a given
bent geometry and level of Pload. 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 Pload. 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, 6Pile Bents
without XBracing 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, 6Pile Bents
without XBracing 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, 6Pile Bents with
XBracing to Resist Ft max design = 12.15k (includes a FS = 1.25)
Critical Uniform Scour, SCR (ft)3,4 No.
Piles
in
Bent
XBracing
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 SingleX 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 SingleX 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 SingleX 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 SingleX 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 DoubleX 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, 6Pile Bents with
XBracing to Resist Ft max design = 12.15k (includes a FS = 1.25)
Critical Uniform Scour, SCR (ft)7,8 No.
Piles
in
Bent
XBracing
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 SingleX 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 SingleX 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 SingleX 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 SingleX 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 DoubleX 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, 6Pile Bents
without XBracing 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, 6Pile Bents
without XBracing 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, 6Pile Bents
with XBracing to Resist Ft max design = 12.15k (includes a FS = 1.25)
Critical Nonuniform Scour, SCR (ft)3,4 No.
Piles
in
Bent
XBracing
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 SingleX 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 SingleX 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 SingleX 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 SingleX 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 DoubleX 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, 6Pile Bents
with XBracing to Resist Ft max design = 12.15k (includes a FS = 1.25)
Critical Nonuniform Scour, SCR (ft)7,8 No.
Piles
in
Bent
XBracing
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 SingleX 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 SingleX 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 SingleX 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 SingleX 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 DoubleX 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 BeamColumn 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 beamcolumn. (See HWL2 and Ft2
positions in Fig. 2.36.)
Before checking the upstream pile for adequacy as a beamcolumn,
consider it as a vertical beam with pinnedends, 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 beamonly 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 fixedend 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 Xbracing, 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 PinnedEnd Condition
107
Fig. 2.38. Upstream Pile, P1, Mmax Values for FixedEnd Condition
108
Fig. 2.39. XBraced Bent with FtLoad at Level of Horizontal Brace
109
The analyses above neglected the axial Pload on the upstream pile. We
now need to consider this load and analyze the pile as a beamcolumn. To do
this we will use the approximate straightline 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 beamcolumn is as
shown in Fig. 2.40. It should be noted that only the bent?s upstream pile is acting
primarily as a beamcolumn with a significant value of M/Mp. Thus, the other
piles in the bent will provide leanon 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
BeamColumn
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 Pload 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+202 = 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 BeamColumn 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
(ftkips)
Mp
(ftkips)
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
Twostory bents will always be Xbraced 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 highwater flood conditions, the HWL and
flood debris raft would be located somewhere in the Xbraced region of the bent.
In this case, the upstream bent pile would not be subjected to significant
bending/beamcolumn 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 Xbraced bents, both singlestory Xbraced and twostory
Xbraced, the upstream bent pile is adequate as a beamcolumn 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 beamcolumn 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 beamcolumn, 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 beamcolumn, summarized above, are
further summarized in more concise flowchart form in Fig. 2.42.
116
Is the bent Xbraced?
Fig. 2.42 Checking Adequacy of Bent Upstream Pile as a BeamColumn
Are the bent piles
larger than HP10x42?
Upstream pile is OK
as a beamcolumn!
No Yes
Is there a source or
history of flood debris
such that a debris raft
could form?
Upstream pile is OK
as a beamcolumn!
Upstream pile is OK
as a beamcolumn!
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 beamcolumn!
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 beamcolumn
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 twostory Xbraced 3 and 4pile 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 Xbracing. 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. GTSTRUDLgenerated
deformation curves for 3 and 4pile 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, 2story, 3pile bent with the lateral load applied at the level of the bent
horizontal brace for the Pload 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. TwoStory XBraced 3Pile 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 2Story XBraced 3Pile
and 4Pile Bridge Bents of Height H=21 ft with HP10x42 Piles and Concrete Bent Cap
with Igross = 41,470 in4 for Symmetric PLoads 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, 1Story XBraced, and 2Story XBraced Bent
Deformations
122
a. Ft loading at Bent Cap
b. Ft loading at Horizontal Brace
Fig. 2.45. GTSTRUDL Generated Deformations of 3Pile Bent from Ft
Loadings
123
a. Ft loading at Bent Cap
b. Ft loading at Horizontal Brace
Fig. 2.46. GTSTRUDL Generated Deformations of 4Pile Bent from Ft
Loadings
124
Table 2.29. Pushover Load, Ft, at Low Position for 2Story XBraced 3Pile
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 Tier1 Screening Tool
Guidelines for some additional expansions of applicability of the Phase II
Report/Tier1 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 6pile bent in the ?ST? having the same HP pile size as the
one being investigated to check the adequacy of bents with more
than 6piles 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
kickout 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 ?kickout? 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 ?kickout? adequacy be retained as is in the Tier2 ?ST?.
126
2.14 Closure
Bent pushover loads for lower levels of Ploads, 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 Pload 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 Pload 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 twostory 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
continuousspan 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, continuousspan 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., simplysupported or
continuousspans
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 10ft. width. These loads are then placed in 12 ft.
traffic lanes spaced across the bridge from curbtocurb. If the curbtocurb width
is between 20 ft. and 30 ft., two design lanes are required, each of which is half
the curbtocurb 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 curbtocurb width, and Fig. 3.1
128
illustrates ?truck lane loadings? and ?design lane loading? on a 32 ft. curbtocurb
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 3traffic lanes.
Otherwise, the LLloading for the pushover loading check should be restricted to
using the actual number of traffic lanes. Also, the most adverse LLloading 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
2Span Continuous 1.25 ?DL 1.25 ?LL
3Span Continuous 1.10 ?DL 1.20 ?LL
4Span 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 simplysupported
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 2Span 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 2Span 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 2Span 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 equalspan
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 4pile bent bridge and Example 2 pertains to a 3pile 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, 4Pile Bents with 2.5? x 2.5? Caps
AASHTO TYPE II GIRDERS
134
Determine BentMax AppliedP
PDL: Deck: Deck Thickness x OuttoOut 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
?Pload to be used above each
pile in pushover analysis
Fig. 3.5. Pushover Load Case I
PLL ? Only UpStream 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 PLoading for 4Pile 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, 3Pile Bents with 2.5? x 2.5? Caps
Determine BentMax AppliedP
PDL: Deck: Deck Thickness x OuttoOut 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
?Pload to be used above each
pile in pushover analysis
Fig. 3.9. Pushover Load Case I
139
PLL ? Only UpStream 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 PLoading for 3Pile Bents
140
CHAPTER 4: REFINED ?ST? AND TIER2 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 ?kickout? 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/2ndedition ?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 2ndtier 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 2ndtier 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 failurecheck 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 beamcolumn when simultaneously
subjected to an axial Pload 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 ?KickOut? and Plunging Evaluation Module (Block 2), slight
refinements in the wording and sequence for indicating the adequacy of bent
piles for ?kickout? were made at the very beginning of the Block. However, no
changes of substance were made in checking for ?kickout?, nor are any followup
screenings indicated for those bents where ?check more closely for ?kickout?
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 secondtier
screenings (Tier2/2) to make assumptions regarding the bent piledriving 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 KickOut 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 Pload 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 XBraced 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 2story bent if member HB1 is
present and for 2story bent if only member HB2 is present
2crl =S+(?H?1?) for 1story bent if HB1 is not present and for
2story bent if HB1 and HB2 are not present
Fig. 4.5b. Transverse Buckling Modes and Equations for XBraced 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 (Tier2/4A and Tier2/4B) 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 fullblown
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 beamcolumn due to a combined axial
Pload 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 Xbraced, 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 beamcolumn
loading. Thus, the possibility of a beamcolumn 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 BeamColumn 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 beamcolumn.
4.3 Second Tier/Tier2 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
Secondtier 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. Secondtier screening for bents for which complete information about
the bent piledriving system are not known, i.e., Tier 2/2A screening, is
154
described in Fig. 4.8a. In this secondtier 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?.
Secondtier screening for bents that do not pass the Scr ? Smax check in
the pile plunging evaluation, i.e., Tier2/2B 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 Tier2/2 screenings, the user should return to, and continue executing, the
ST.
4.3.2 Pile Buckling Evaluation 2nd Tier Screening
Secondtier 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
?kickout? 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 Tier2/2A 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 ftkip 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. Tier2/2A Screening for Pile Plunging Adequacy Assessment
156
In recognition of the facts that,
? the most heavily loaded pile in a bent will get ?leanon?
plunging support from the adjacent piles in the bent
? for continuous span bridges, the most heavily loaded bent will
get ?leanon? support from the adjacent supports/bents
? the loading of all possible Design Traffic Lanes (see Table 3.1
in Phase IIIScreening 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. Tier2/2B Screening for Pile Plunging Adequacy Assessment
157
4.3.3 Bent Pushover Evaluation (Block 4) 2nd Tier Screening
Secondtier 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. Tier2/4A screening, is given
in Fig. 4.9a. Secondtier screening for bents that do not pass the Scr > Smax
check in the bent pushover evaluation, i.e., Tier2/4B 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 continuousspan 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 6pile bent with or without Xbracing 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 Tier2/4A 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 Tier2/4B 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 Tier2, 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 Tier2 screening. Bents not checked via the
?ST? to date, should be checked using the Phase III refined ?ST?.
It is anticipated that the Tier2 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 followup Tier2 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 TIER2 ?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 Tier2 screenings for this module. Also, in the KickOut and
Plunging Evaluation Module (Module 2), there are no changes in the ?ST?
regarding the check for ?kickout? failure and there are no Tier2 screenings for
those piles/bents identified as possibly having a ?kickout? 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., Tier2 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 Tier2 screenings for buckling. It is anticipated that the Tier2
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?, Tier2 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 Tier2 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 Tier2 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 Tier2
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
?kickout? 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, 8pile (or more) bents with piles in a
single row with or without Xbracing 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 Tier2 Pile Plunging Failure Check
Given below are some example applications of the refined/2nd edition ?ST?
checks for possible pile/bent plunging and kickout failures. It should be noted
that the refined ?ST? is the same as the original ?ST? regarding checking for
pile/bent ?kickout? 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 kickout
failure. However, for the pile plunging check, the refined ?ST? includes two Tier2
pileplunging checks, and these are emphasized in Examples 1 and 2 below.
164
Fig. 5.1. Example Problem 1 for KickOut and Plunging
165
Fig. 5.2. Example Problem 1 for KickOut and Plunging (Continued)
166
Fig. 5.3. Example Problem 1 for KickOut 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 Tier2 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, 2ndtier
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 Tier2 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 Pload levels of P=60k and 80k acting on the cap
? Reduced Pload 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 Tier2 pushover screening checks. Example
Applications 6, 7, 8 and 9 below focus on the Tier2 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 BeamColumn 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 beamcolumn from a
combined axial Pload 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 BeamColumn
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 5.35.5 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 Tier2
screening process. Section 5.6 provides an example application check of a
bent?s upstream pile for a possible beamcolumn failure due to a combined axial
Pload 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 secondtier of screening to use as a followup for
those cases where the ?ST? indicates, ?Bent should be
looked at more closely for possible plunging, buckling, or
pushover 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 Pload Due to Flood Water Lateral Loading
Analyses that were undertaken to determine these additional Ploads (?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
3pile 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 Pload need not be considered when determining Ploads 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 3pile or
4pile 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 Pload Levels
Pushover loads in the Phase II ?ST? were determined for various bent
geometries, pile sizes, scour levels, and bracing conditions for Ploads (one
applied to the bent cap above each pile) of {P} = {100k, 120k, 140k, 160k}.
However, for some smaller bridges, the Ploads 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 3pile and 4pile bents for Ploads 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 Ploads somewhat less
than 80k.
6.2.5 Pushover Loads for Unsymmetric Pload Distribution
Pushover analyses in the Phase II ?ST? assumed a uniform Pload
distribution across the bent cap, as indicated in the subsection above. These
analyses, along with the additional smaller Pload levels of the previous
195
subsection, produced pushover analyses results for a uniform Pload distribution
for Ploads of {P} = {60k, 80k, 100k, 120k, 140k, 160k}. However, it was not clear
that a uniform Pload distribution yielded a smaller bent pushover load, Ft, than
an usymmetric Pload distribution, even though it provided the larger gravity bent
loading. It was reasoned that a smaller unsymmetrical Pload 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 narrowwidth 3pile and 4pile
bents, thus these two pile bent configurations were considered when checking
the pushover loads for unsymmetric Pload distribution. The results of pushover
analyses for the 3 and 4pile bents with unsymmetric Ploads 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 Pload. Figures 2.26 ? 2.29 graphically illustrate the small difference
in pushover load between the unsymmetrical and symmetrical Ploading cases.
Even though the unsymmetrical distribution gives somewhat smaller pushover
loads, and earlier screenings via the Phase II ?ST? assumed a uniform Pload
distribution, the fact that the difference in pushover load between the two Pload
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 4pile 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 Pload and variable
scour occur together and reflects a greater pushover capacity for this case when
compared to that of a uniform Pload 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 tipover 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 4pile
bents with the debris raft water loading, Ft, applied at the location of the bottom of
the Xbracing for singlestory bents and at the height of the horizontal strut
located between the upper Xbracing and lower Xbracing for 2story 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 Xbracing, 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 BeamColumn
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 beamonly member and as a beamcolumn member. These checks
are shown in Section 2.11. In all situations, the upstream pile is adequate when
198
checking as a beamonly 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 2ndtier screening (Section 4.3) is
included in this report; this 2ndtier 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 Tier2 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 bentsupported 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 ?kickout? 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 beamcolumn due to a
combined Pload 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 930585, 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 930608, 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 930608 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 930608 Report, January 2006.
202
Hughes, D. and Ramey, G.E., ?Stability of Highway Bridges Subject to Scour 
Phase II  Part II: Bridge Bent PDelta Curves in Transverse Direction Using
FBPier and GTSTRUDL Pushover Analysis Procedures?, Alabama
Department of Transportation Project 930608 Interim Report, June 2005.
203
APPENDIX A: EXAMPLE GTSTRUDL INPUT CODE FOR PUSHOVER
ANALYSIS FOR VARIOUS BENT CONFIGURATIONS
204
Example 1: 3Pile 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: 4Pile Bent, Braced, Unsymmetric Load, Symmetric Scour
STRUDL ' '
$$
$$ This GTSTRUDL file created from GTMenu on 3/20/2007
$$
UNITS INCH KIPS DEG FAH
JOINT COORDINATES GLOBAL
1 22.5 180
2 120 180
3 216 180
4 358.5 180
5 24 196
6 120 196
7 216 196
8 312 196
9 5.25 42
10 330.75 42
11 21.75 174
12 314.25 174
13 120 90.0857142857
14 216 90.0857142857
15 120 130.314285714
16 216 130.314285714
TYPE SPACE FRAME
MEMBER INCIDENCES
1 5 6
2 6 7
3 7 8
4 1 9
5 9 11
6 11 5
7 2 13
8 13 15
9 15 6
10 3 14
11 14 16
12 16 7
13 4 10
14 10 12
15 12 8
16 11 15
17 15 14
18 14 10
19 9 13
20 13 16
21 16 12
UNITS INCH KIPS DEG FAH
MEMBER PROPERTIES PRISMATIC AX 864 IX 1000000 IY 1000000 IZ
41472
1 2 3
MEMBER PROPERTIES TABLE 'M/S/HP9 ' 'HP12x53 '
4 5 6 7 8 9 10 11 12 13 14 15
MEMBER PROPERTIES TABLE 'CHANNEL9 ' 'C4x7.25 '
16 17 18 19 20 21
STATUS SUPPORT 
207
1 2 3 4 5 6 7 8
UNITS INCH KIPS DEG FAH
JOINT RELEASES
1 2 3 4 MOM X Y Z
5 6 7 8 FOR X Y MOM Z
UNITS INCH KIPS DEG FAH
CONSTANTS
BETA 90 
4 5 6 7 8 9 10 11 12 13 14 15
MEMBER RELEASES
16 17 18 19 20 21 START MOM Y Z END MOM Y Z
MATERIAL STEEL
MATERIAL CONCRETE 1 2 3
UNITS INCH KIPS DEG FAH
LOADING 'CONST'
JOINT LOADS FOR Y 80
5 6
JOINT LOADS FOR Y 53
7 8
UNITS INCH KIPS DEG FAH
LOADING 'INCR'
JOINT LOADS FOR X 1
5
NONLINEAR EFFECTS
GEOMETRY ALL MEMBERS
PLASTIC HINGE 
FIBER GEOMETRY NTF 1 NTW 1 NBF 8 ND 8 LH 3.0 
STEEL FY 36.0 ESH .124 ESU .2 FSU 36.001 ALPHA 0.0 
MEMBER 4 5 6 7 8 9 10 11 12 13 14 15
PLASTIC HINGE 
FIBER GEOMETRY NTF 1 NTW 1 NBF 8 ND 8 LH 3.0 
STEEL FY 16.1 ESH .124 ESU .2 FSU 16.101 ALPHA 0.0 
MEMBER 16 17 18
LOAD LIST ALL
PUSHOVER ANALYSIS DATA
CONSTANT LOAD 'CONST'
INCREMENTAL LOAD 'INCR'
MAXIMUM NUMBER OF LOAD INCREMENTS 100
MAXIMUM NUMBER OF TRIALS 20
LOADING RATE 1.000000
CONVERGENCE RATE 0.500000
CONVERGENCE TOLERENCE COLLAPSE 0.000100
CONVERGENCE TOLERANCE DISPLACEMENT 0.001000
MAXIMUM NUMBER OF CYCLES 50
DISPLACEMENT CONTROL OFF
END
PERFORM PUSHOVER ANALYSIS
208
Example 3: 5Pile Bent, 2Story, Braced, Symmetric Load, Unsym. Scour
STRUDL ' '
$$
$$ This GTSTRUDL file created on 1/ 25/2008
$$
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: 6Pile Bent, Double XBraced, 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