Structural performance assessment of an existing reinforced concrete building retrofitted with inverted Y-shaped braces

In this study, the efficiency of inverted Y-shaped eccentric steel bracing systems with different link lengths for seismic retrofitting of seismically insufficient reinforced concrete building were investigated. For this, since most of the buildings in the existing building stock of our country were constructed before 1998 and were designed according to 1975 seismic design code, firstly, a reinforced concrete building having a symmetric geometry in plan in compliance with 1975 seismic regulation was selected as a case study. As a retrofit scheme, inverted Y-shaped braces were inserted into the external bays of the existing building. In the seismic strengthening of the original building, inverted Y-bracing was designed considering three different steel link lengths. The analytical frame model having nonlinear properties of structural members of the existing and retrofitted buildings was performed. The performance of the existing and retrofitted structures under earthquake loading was comparatively examined through nonlinear static and nonlinear time history analyses. From the results of the analysis, it was found that the seismic performance of the existing reinforced concrete building with inadequate detailing exhibited considerable improvement after retrofitting with eccentric braces. The results also indicated the importance of the selection of the link length in the design of inverted Y-shaped eccentric steel braces for seismic retrofitting.