Seismic collapse assessment of K-shaped bracings in cold-formed steel frames

Abstract

K-shaped bracing is one of the lateral load resisting systems used in Cold-Formed Steel structures. Recently, some researches have been conducted to obtain further information about the seismic performance of the CFS using K-shaped bracings under monotonic and cyclic loads. In this research, the seismic performance factor of this structural system is under study. To determine the proper value of this factor, a non-linear finite element model of this structural system is developed using OpenSees software, and the cyclic behavior of this model is verified with previous experimental results. Several structures designed in accordance with Iranian seismic code were modeled using the verified model, and incremental dynamic analysis is performed on these structures. The analysis was performed according to FEMA P695 procedures using a ground motion set consisting of 22 earthquake records. Eventually, the studies showed that the seismic performance factor of 2 is a proper value for the cold-formed steel frames with K-shaped bracings. Also, as another result, the increase in the number of stories and the site’s seismic risk will increase the structure’s collapse probability. Furthermore, the height limitation proposed by seismic codes for this system seems to be somewhat conservative and it can be concluded that usage of the K-shaped bracing system is possible for taller structures in zones with low seismicity risk. Finally, it can be concluded that the K-shaped bracings might not have a suitable performance due to ductility issues.