Effects of cyclic strain hardening on performance of eccentrically braced frames

Abstract

Performance based seismic design (PBSD) procedures have been developed in recent years. Studies conducted in the past revealed that strain hardening ratio (SHR) used in numerical modeling can be influential on the performance of steel structural systems. In this paper, the effects of SHR on the performance assessment of eccentrically braced frame (EBF) buildings were studied by using FEMA P-58 methodology. The numerical model was validated using the pseudo-dynamic test results of the DUAREM structure. Seismic performance of six archetype EBFs with different number of stories and link length to bay width (e/L) ratios were evaluated under design basis earthquake (DBE), maximum considered earthquake (MCE), and collapse level earthquake (CLE). Irreparable residual drift, repair cost and unsafe placards were calculated for SHR ranging between 0 and 0.01. The results showed that the residual interstory drift ratio is more influenced by the SHR when compared with the interstory drift ratio, link rotation angle and story acceleration. The replacement decision was found to depend on the SHR, the number of stories, the e/L ratio, and the seismic hazard. Under MCE and CLE level events, almost all of the archetypes with SHR ≤ 0.003 required replacement while replacement can be avoided for some of the archetypes with SHR > 0.003. Under DBE level events, 3-story archetypes and 6-story archetypes with SHR ≥ 0.002 did not require replacement. Nine-story archetype with e/L = 0.08 required replacement for SHR = 0 only, while archetypes with e/L = 0.12 required replacement for SHR ≤ 0.003. The study demonstrated the strong influence and sensitivity of the repair cost to the SHR.