Development of a Single-Degree-of-Freedom Algorithm for the Analysis of Buried Composite Pipes Subjected to Internal Dynamic Pressure
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The overall objective of this research project was to develop a practical engineering methodology for the analysis of underground composite pipes subjected to internal dynamic loading. The need for this analytical methodology has been emphasized by events such as accidental gas line explosions that have resulted in extensive property damage and injuries, and the detonation of explosive devices placed in drainage culverts to harm vehicle occupants on the roadway above the pipe. The loading was considered to be sufficient to rupture the pipe and cause significant acceleration of the ground surface. The analytical tool developed is intended to aid in the design of high-strength composite pipes that can resist internal high-order explosions. Static models of composite pipes were developed using Abaqus finite element (FE) software with shell elements formulated for analyzing composite materials. The finite element results were used to establish “effective” nonlinear stress-strain relationships for each type of pipe considered, which varied by fiber type, fiber stacking sequence, and pipe diameter and thickness. The generalized stress-strain relationships were then used to compute pressure-displacement relationships based upon fundamental thin-walled pipe mechanics theory. A dynamic analysis approach was then implemented, based upon a single-degree-of-freedom (SDOF) model in which the resistance was represented by the nonlinear pressure-displacement relationship of the pipe and the mass was represented by a soil prism mobilized by the dynamic loading plus the weight of any objects positioned above the pipe. In order to solve the equations of motion, algorithms were programmed in a user-friendly worksheet format that utilized the central difference method to advance the solution with time. Time domain displacement, velocity, and acceleration response curves were generated for a wide range of input parameters. From these results, general trends and conclusions were drawn toward identifying the parameters that most affect the blast resistance of buried composite pipes. Finally, the implementation of the methodology was illustrated using two design scenarios.