Seismic fragility assessment of reinforced concrete moment frames retrofitted with strongback braced system

Abstract

This study focused on analysing the seismic fragility and retrofitting of reinforced concrete flexural frames using strongback braced system. Using the steel strongback braced system as a means of seismically strengthening and retrofitting reinforced concrete moment frames (RCMFs), this research aims to enhance the effectiveness of RCMFs. In this study, RCMFs of 5-, 10-, and 15-stories are designed according to the first and fourth editions of the Iran Earthquake Standard 2800. The RCMFs designed according to the first edition are strengthened and reinforced using the SB system. The studied structures were analyzed under incremental static loading and time history analysis. The results show that the yield force and maximum base shear for the structures designed with the fourth edition, compared to the structures designed with the first edition, have increased by 1.28–1.42. This demonstrates the necessity of improving structures constructed according to the first edition. Meanwhile, the results of the retrofitted structures with strongback braces show the same or better performance than newly designed structures. The results of the fragility analysis show that the addition of the strong bracing system significantly improves the performance of the structures and brings them closer to the 4th edition standards. The retrofitting system reduces drift ratio between floors and reduces structural damage.

Keywords

• Strongback braced (SB) system
• Reinforced concrete moment frames (RCMF)
• Strengthening
• Retrofit
• Incremental static/dynamic analysis
• Seismic fragility analysis