Author(s)

Y. E. Ibrahim

Abstract

Seismic codes for buildings are being revised worldwide after the occurrence of recent earthquakes that has led to the realization that these codes are not sufficiently definitive in terms of design requirements as well as structural performance. Accordingly, it may be the case that buildings that were designed according to old seismic codes need to be rechecked to provide information on the predicted performance of existing structures. If performance enhancement under potential earthquakes is deemed necessary for a particular structure, retrofitting may be required. This can be achieved by increasing the lateral stiffness of the structure by increasing the columns’ dimensions and reinforcement, adding steel braces or through using energy dissipating devices. In this research, finite element analysis is used via the software SeismoStruct to study the effectiveness of retrofitting existing multistory reinforced concrete framed structures in improving structural seismic performance. To this end, three models were analyzed: 4-story, 8-story and 12-story reinforced concrete framed structures, designed according to Saudi Building Code (2007) for vertical loads and seismic forces for 0.2-second and 1.0-second response spectral accelerations of 0.21g and 0.061g, respectively. Two retrofitting techniques are considered to upgrade the structures to withstand seismic forces for 0.2-second and 1.0-second response spectral accelerations of 0.66g and 0.23g, respectively, which represent the highest spectral accelerations in KSA based on the current code. The study included nonlinear static pushover analysis and incremental dynamic analysis using records of twelve artificial and historic earthquakes. The results showed that retrofitting techniques using column jacketing and steel braces enhanced the structural response of all models. The efficacy of using steel braces is better than for column jacketing in almost all analyzed cases.

Keywords

retrofitting, incremental dynamic analysis, nonlinear static pushover analysis, reinforced concrete frames, steel braces