Evaluation of Steel Concentrically Braced Frames under Far-Fault Earthquakes

Concentric bracing systems with V and inverted-V configurations are favored in architectural design due to their ability to create wider openings and provide greater flexibility, especially in open-plan layouts or transparent facades. This study evaluates the seismic performance of such steel braced frames under far-field ground motions. A six-story steel structure with typical design characteristics was modeled and analyzed using nonlinear dynamic analysis with a set of ۲۲ pairs of real earthquake records. The structural design followed the ASCE ۷-۲۲ and AISC ۳۴۱-۲۲ provisions, with special attention to the impact of unbalanced forces induced by bracing members. The common assumption that these forces cancel out in adjacent stories was critically examined, revealing that this is not always a conservative assumption, as differences in buckling and pre-buckling compressive strength between stories may lead to uneven force distribution. The results showed a non-uniform drift distribution across the stories, with significant concentration of deformation in intermediate and upper levels, indicating the potential for soft-story formation and progressive damage. Furthermore, notable discrepancies between elastic analysis results adjusted by the Cd factor and nonlinear time history results were observed, especially in the upper stories. The findings contribute to a better understanding and design optimization of concentrically braced frames with architecturally driven configurations.

کلیدواژه ها:

Concentric braced frame (CBF) ، V-bracing ، Inverted V-bracing ، Far-field earthquakes ، Unbalanced forces