Reliability of steel structures with Chevron bracing systems considering the performance-based seismic design philosophy

In this paper, the seismic performance and reliability of steel buildings with Chevron-Braced frames are studied integrating a novel probabilistic approach and the performance-based seismic design concept. The seismic response of models is extracted using response history analyses with the help the commercial software SAP2000. In this sense, three variables associated with the seismic response of the structure are studied: overall lateral displacement, rotation of connections, and inter-story drift. Those responses are evaluated by exciting the structure with eleven characteristic ground motions of the zone with respect to three performance levels: immediate occupancy, life safety, and collapse prevention. Once the seismic response is extracted for every performance level, the reliability of the models is calculated with respect to inter-story drift as described next. First, considering the seismic response in terms of inter-story drift for every ground motion, the associated histogram is constructed. Then, using 13 Probability Density Functions (PDFs), a Chi-square test is performed to identify the best-fitted PDF associated to the histogram of inter-story drift. Afterwards, with the best-fitted PDF of inter-story drift, the probability of failure and reliability index are extracted considering serviceability limits for every performance level. This represents a unique approach to extract the risk of structures subjected to ground motions associated to different performance levels. In addition to the structural reliability, a study about the cost of the structures with and without Chevron braces is developed, and then, it is documented the best option. Finally, based on the results reported in this paper, it is demonstrated that steel buildings with Chevron-braced frames present a better seismic performance than steel moment resisting frames without any bracing system. In summary, overall lateral drifts are reduced between 40 and 60% when Chevron braces are implemented in comparison to steel moment resisting frames without braces. On the other hand, if Chevron bracing systems are not used, i.e., in steel moment resisting frames, the inter-story drifts are about 300% higher than those of steel structures with Chevron braces. Hence, structural damages can be considerably reduced if Chevron-braced frames are implemented in steel structures that may be excited by characteristic ground motions of the zone where they are located.