Evaluating Procedure of Optimal Seismic Retrofit Level for a Low-Rise Reinforced Concrete Building

This study proposes an estimating procedure that can be used to set the optimal seismic level in the seismic retrofit design for a low-rise reinforced concrete (RC) building. Along with damage control, the cost of maintenance over the remaining service life is also considered in the estimating procedure. However, when a seismic retrofit level defined by the ground acceleration corresponding to the ultimate deformation of the single degree of freedom (SDOF) system for a selected building is specified, several seismic retrofit methods can be used to achieve the specified seismic retrofit level. Since their respective maintenance costs differ, the average value of the annual costs of maintenance for a specified seismic retrofit level was adopted. Under the condition that the average value of the annual reliability indices of a seismic retrofit level for a specified damage state needs to be equal to or greater than the allowable annual reliability index, the seismic retrofit level corresponding to the minimal value is regarded as the optimal level. Finally, a case study was used to discuss the application of the estimating procedure for the optimal seismic retrofit level proposed here. In addition, combinations of the upgrading rates in yielding acceleration and the ductility capacity of the SDOF system are also suggested to the designer of the retrofit for the selected building.