Seismic retrofit of a soft first story structure using an optimally designed post – tensioned PC frame

In this study, the seismic performance of a self-centering post-tensioned precast concrete (PC) frame with an enlarged beam end is evaluated for retrofit of a soft first story structure. A finite element model of a post-tensioned beam-column assembly with an enlarged beam end is validated by comparison with experimental results, and is used to validate an analytical model of the proposed system. Then the analytical model is used to retrofit a soft first story structure with only columns in the first story and infill walls above. A multi-objective optimization of the retrofit system is carried out using genetic algorithm. The seismic performance of the retrofitted structure is assessed by incremental dynamic analysis and fragility analysis. The analysis results show that the retrofit system calibrated by the optimization procedure is effective in increasing the seismic performance of the soft first story structure.