Analytical Study of Zone Of Plastic and Cracked Region in Slender Bridge Piers Using Finite Element Method

Abstract

The performance of slender bridge piers when subjected to lateral loads acting simultaneously with axial loads is a significant issue faced by the bridge design industry. For such piers the interaction of flexural ductility with the variation in lateral and longitudinal reinforcement is not well established. The precise height up to which lateral confinement should be provided to ensure adequate ductility in seismic scenarios is still a topic of research for slender piers. While most of the international codes have given general guidelines for the height of lateral confinement in bridge piers , the adequacy of these guidelines is still doubtful when it comes to slender bridge piers. This dissertation includes the analytical study done on twenty-seven slender bridge pier models to determine the extent of critical plastic and cracked zone at the base . Nonlinear static analysis is performed in the present study in which the pier is subjected to lateral deformation along with axial force applied simultaneously using MIDAS FEA software package both without incremental load steps and with five incremental load steps. The effect of variation in percentage of longitudinal reinforcement, shear reinforcement and axial load ratio on the plastic and the cracked zone is studied, keeping the cross section of pier and the grade of steel and concrete same for all the models. The results obtained after analysis e.g. height of fully open , partially open cracked zone and the height of plastic zone are graphically represented and the effect of one of the factors on these heights keeping other two factors constant is studied. Also, the length up to which the lateral confinement required for ductility demand of bridge piers is determined based on the height of plastic zone obtained for each model and the same is compared with existing international codal provisions. It was observed that the maximum height of plastic zone obtained in the present study is more than the maximum height of lateral confinement suggested by various international guidelines. This observation indicates that the current codal provisions for height of lateral confinement are not fully reliable for slender bridge piers and hence these guidelines need to be revised after more detailed and diagnostic study.