Seismic Damage and Collapse Assessment of Composite Moment Frames

Abstract

Damage and stability assessment techniques are developed for evaluating the seismic performance of composite steel-concrete moment frames. The approach features a new seismic damage index based on cumulative member ductility that employs the concept of primary and follower load cycles to distinguish loading history effects. Equations are presented to determine the limiting rotation capacity for RC columns, steel and composite beams, and composite steel-concrete connection subassemblages, and the resulting damage model is validated by comparisons with published test data. The damage index is incorporated in a methodology that combines nonlinear time history and gravity load stability analyses to evaluate collapse prevention performance as a function of earthquake ground motion intensity. In contrast to existing seismic assessment procedures, the proposed methodology integrates the destabilizing effects of local damage indices to evaluate overall system response. The assessment technique is illustrated through a trial design study of a six-story frame conducted under Phase 5 of the U.S.–Japan Cooperative Research Program on composite and hybrid structures.