Seismic performance assessment of hybrid braced cold-formed steel walls

Cold-formed steel (CFS) structures or light weight steel frame (LSF) structures have been frequently used in recent years due to their fast constructions as well as consumed light weight steels. CFS structures are constructed with light thin cold formed steel members. Lateral loading systems of these structures are often steel or wooden shear walls and merely tensional steel cross-straps in the form of shear panels. In the other words, shear panels form the main components of such structures in providing seismic performance. The performance of lateral loading system with hybrid bracing is evaluated in this study considering the simultaneous use of steel shear wall and strap cross-bracing in different floors of a CFS structure. For this purpose, nonlinear static analysis, linear dynamic analysis and incremental dynamic analysis (IDA) have been conducted on 1-3 storey frames with shear wall, steel strap cross-bracing and hybrid bracing using OpenSees software. Response modification factor (R) is one of the most important seismic parameters of structures against earthquake loads. In fact it shows the capability of structural system in absorbing and dissipating the energy caused by earthquake and creating nonlinear deformations without total collapse of structure. This factor has been calculated here for the mentioned lateral bracing systems. The obtained values are 4.1 and 3.1 for CFS structures with shear wall and cross-bracing, respectively, and 4.9 and 2.8 for hybrid bracing considering the shear wall and bracing in the lower storeys, respectively. Based on the results of this research, it seems that hybrid bracing of shear wall in the lower storeys is one of the best lateral bracing system for cold-formed steel structures.