Quantification of seismic performance factors of the buildings consisting of disposable knee bracing frames

Abstract

Braced frames are prevalently utilized as lateral load resisting systems in common engineering practice. disposable knee bracing (DKB) frames are categorized as one of the well-known types of these frames. In such systems, braces provide stiffness, while the link elements play an important role as an energy-absorbing fuse. During an extreme loading, link members help the structure to dissipate the imposed energy by plastic deformations. In this research, bracing frames took advantage of shear and/or flexural link elements. The previous experimental results revealed that hysteresis behavior of link elements remains constant until a specific rotation. Hence, employing such links as parts of a lateral load resisting system can increase the energy absorption capacity of the system. However, designing structures with DKB frames based on common design guidelines demands for evaluating required design factors for these braced frames. Seismic performance factors such as response modification factor (R), over strength factor (Ω), Deflection amplification factor (Cd) and Ductility factor (μT) are required first to design any structural system. In order to quantify these factors for the intended braced frames, the procedure introduced in FEMA P695 was used in this research. Numerous archetype frames were designed based on assumed performance factors. The behavior of archetype frames were then examined through performing push-over and incremental dynamic analyses. Some indexes such as the collapse margin ratio and the adjusted collapse margin ratio were defined and calculated for the archetype frames based on the nonlinear analyses results. The values of the calculated indexes were eventually compared with the accepted values proposed by FEMA P695 to validate the presumed seismic performance factors of DKB systems.