Seismic behavior and retrofitting of reinforced concrete moment resistant frames

Many multistory reinforced concrete frame structures built prior to 1970's located in seismic zones have been designed only for gravity loads without any considerations for lateral loads. These structures are referred to as Gravity Load Designed (GLD) frames. The lack of seismic considerations in GLD structures results in non-ductile behavior that may cause the lateral load resistance of these buildings to be insufficient for even moderate earthquakes. Based on the current Canadian practice as prescribed by CAN3-A23.3 1994, reinforced concrete structures located in seismic zones should be designed as ductile or nominally ductile frames. In this study, a typical 5-story frame building is designed as (a) ductile, (b) nominally ductile and (c) GLD frame. Analytical investigation is performed to evaluate and to compare the performance of each frame. The study includes "pushover" analysis and non-linear time-history analysis. The results in terms of story displacement, ductility, shear, drift, sequence of cracking and yielding and the damage potential are presented. As a result of the poor performance of the GLD frame, it is retrofitted with fiber-reinforced polymers (FRP). Different retrofitting schemes using FRP are used to compare the behavior in terms of ductility. In this study, the behavior of the retrofitted frame is compared with the that of the GLD frame. Based on the results of this study, a guideline for improving the seismic performance of reinforced concrete frame structures is provided.