Seismic Design of Post-Tensioned Precast Segmental Bridge Column

Over the past 20 years, the use of the precast modulus construction for accelerating bridge construction has gained attention increasingly in the U.S.A and Europe. Besides the acceleration of bridge construction, the precast modulus construction has advantages to prevent accident occurred, reduce traffic disrupt, and reduce impact to the environment, to ensure the construction quality and to minimize the life-time cost. However, most of the applications have been in the low-seismicity regions. In high-seismicity regions such as California in the U.S. or Taiwan, there is nearly no application or design code provided. Therefore, the behavior study of precast segmental bridge column and the concept of strength reduction factor are attributed in this study to carry out the design recommendation.
There are two parts in this study. The first one is the investigation of strength reduction factor. From the previous study, the energy dissipation capacity of precast segmental bridge column is smaller than that of traditional bridge column. Under the same earthquake excitation, the strength reduction factor for precast segmental bridge column should be smaller than that for traditional one to achieve the same ductility demand. In this study, nonlinear dynamic SDOF analysis was involved, and 36 different ground motions were used in this analysis to investigate the proper strength reduction factor for precast segmental bridge column. In the analysis, bilinear plastic (BP) hysteretic model and stiffness degrading self-centering (SDSC) hysteretic model were used to present the behavior of traditional bridge column and precast segmental one, respectively. According to the result, it was proved that the strength reduction factor of precast segmental bridge column is smaller than that for traditional one. The ratio of strength reduction factor for SDSC model with different energy dissipation capacity and different ductility demand to that for traditional one was meshed up to modify the strength reduction factor formula provided in current seismic codes.
The second part is the investigation of energy dissipation and ductility capacity of precast segmental bridge column. According to the first part result, energy dissipation capacity and ductility capacity are crucial to select the appropriate strength reduction factor for precast segmental bridge column. The unbonded length of energy dissipation bar can be used to prevent the energy dissipation bar from premature fracture, and the ductility demand can develop. In this study, the unbonded length used to achieve the ductility demand was carried out. The amount of energy dissipation bar ratio used in precast segmental bridge column effects the amount of energy dissipation capacity. To investigate the relationship, a sequence of parametric analysis is processing in finite element model constructed by the finite element analysis software ABAQUS. After the energy dissipation capacity and ductility capacity are specified, the strength reduction factor can be selected properly in design of precast segmental bridge column.
The last part is design example. Depending on the analysis result of this study, a complete design procedure and a design example are proposed, which provide engineer with a simple method to design precast segmental bridge columns. The procedure and equation for designing purpose are verified to be reasonable. It may be applicable in practical engineering cases in the future.