Functional Recovery of Steel Special Moment Frames

Abstract

Steel special moment frames (SMFs) designed per current codes will likely require major repair or be a total loss after design earthquake (DE) shaking. Functional recovery of SMFs can be improved by designing to stricter drift limits, improving postyield stiffness, or improving repairability. In this study, FEMA P-58/ATC-138 (beta) was used to determine the most effective option for improving functional recovery. Eighteen SMFs were designed with different heights (4, 6, and 8 stories), different risk categories (II and IV), and different connections (with varying postyield stiffness and repairability) and were analyzed under response history analysis (RHA). Results from the RHA were used in the FEMA P-58/ATC-138 (beta) analyses to quantify functional recovery for each design. The building designs showed that 6- and 8-story SMFs designed for Risk Category IV were 1.8 to 2.2 times heavier than Risk Category II designs, and that the direct cost premium for Risk Category IV design (versus Risk Category II) was 4%–14% of the total building costs. Response history analysis showed that SMFs with enhanced postyield stiffness had up to 47% lower residual drifts than SMFs with typical postyield stiffness. FEMA P-58/ATC-138 (beta) analyses showed that SMFs with enhanced postyield stiffness and repairability designed to Risk Category II had functional recovery comparable to Risk Category IV SMFs with typical postyield stiffness and repairability. While some proposals to improve functional recovery focus primarily on stiffness and strength, this study demonstrates the relative value of postyield stiffness and repairability.