On the quantification of seismic performance factors of Chevron Knee Bracings, in steel structures

Abstract

As a matter of fact, it is necessary to have the values of Response Modification Factor R, Over-strength Factor Ω0, and Deflection Amplification Factor Cd in order to design seismic-force-resisting systems according to design and loading codes. This study is intended to evaluate these factors for a structural lateral bracing system called Chevron Knee Bracing (CKB). In this type of bracing, the knee elements assist the system to dissipate energy through the formation of plastic flexural and/or shear hinges within the presented bracing system. The approach utilized in this study is according to FEMA P695 based on low probability of structural collapse and involves nonlinear static and dynamic analyses. Over-strength and ductility of this type of bracing is investigated through performing nonlinear static analyses. Conducting Incremental Dynamic Analyses (IDA), Collapse Margin Ratios (CMRs) of the defined archetypes model are achieved and modified to obtain an Adjusted Collapse Margin Ratio, ACMR for each archetype. The values of calculated ACMRs are compared with the accepted values proposed by FEMA P695 in which the total system collapse uncertainty is considered to prove the validity of presumed seismic performance factors of CKB systems.