Structural reliability of steel buildings with X-bracing systems considering the performance-based seismic design philosophy

The main objective of this paper is to study and compare the structural reliability of steel moment resisting frames (SMRFs) and steel frames with X-bracing systems considering the performance-based seismic design (PBSD) philosophy. In this sense, to accomplish such a study, nonlinear response history analysis is implemented. The buildings under consideration are designed to be located in Culiacan, Mexico. The results are presented in terms of overall displacements, rotations of connections, and interstory drifts, for three performance levels: (1) immediate occupancy, (2) life safety, and (3) collapse prevention, respectively. For each performance level, 11 ground motions were selected to study the response of the structures. Such responses were extracted by using the SAP2000 commercial software to perform structural analysis. It was demonstrated that the steel frame with X-bracing systems developed a better seismic performance than SMRFs for all three variables under consideration. In addition, it was found that a reduction up to 70% in overall displacements and interstory drifts can be achieved when X-bracing systems are used in steel structures. The risk of the structures was extracted in terms of reliability index and probability of failure considering probability density functions of interstory drifts. It was demonstrated that reliability index increased for structures with X-bracing systems in comparison with SMRFs. Finally, in terms of costs, steel structures with X-bracing systems are more expensive than SMRFs. However, its use is justified because serviceability conditions as overall displacement and interstory drift are considerably reduced.