0746 1 Graduate Research Assistant, John A. Blume Earthquake Engineering Center, Stanford University, Stanford, CA 94305-4020 2 Associate Professor, John A. Blume Earthquake Engineering Center, Stanford University, Stanford, CA 94305-4020 ASSESSING SEISMIC PERFORMANCE OF COMPOSITE (RCS) AND STEEL MOMENT FRAMED BUILDINGS Sameh S F MEHANNY 1 And Gregory G DEIERLEIN 2 SUMMARY Investigated is the seismic performance of composite special moment frame systems composed of reinforced concrete columns and steel beams. A composite building, designed according to recently proposed seismic design standards, is analysed by static push-over and nonlinear time history analyses under a series of ground motions (two bins of general and near-fault records with forward directivity) at different hazard levels. A new technique is presented by which local seismic damage indices are computed at the structural component level and then integrated through a global frame stability analysis under gravity loads. Stability and drift indices are related to performance levels suggested by codes and to a comparable structural steel moment frame design. Both the steel and RCS frames are shown to consistently exceed the life safety and near collapse performance levels implied by current building codes. Also presented are suggestions for additional ground motion parameters, beyond the standard intensity index of spectral acceleration, that can reduce uncertainties in estimating median response with a limited set of nonlinear time history analyses. INTRODUCTION Over the past twenty years, composite moment frame building systems, or so-called RCS frames consisting of reinforced concrete (RC) columns and steel beams, have been used in the US and Japan as a cost-effective alternative to traditional structural steel or RC construction (Griffis 1992). Compared to high-rise steel buildings, RCS systems offer more efficient use of materials, a reduction in total construction time, and the elimination of field welding at beam-column connections. The latter helps avoid fracture problems experienced with welded steel connections that were observed after the Northridge earthquake. In spite of the advantages of RCS systems, their use in high seismic regions has been constrained by the lack of design information on composite component behavior and inelastic system performance. Accordingly, one goal of this study is to demonstrate the reliable seismic response of RCS frames. This in turn requires modern ways to quantify their performance. Based on a more complete study by Mehanny (1999), the goals of this paper are to (1) review capabilities of models developed by the authors to analyze RCS and steel moment frames, (2) propose damage indices and performance criteria to assess seismic performance of RCS frames under multi-level earthquake hazards, and (3) evaluate the seismic performance implied by building code requirements for RCS frames in the 1997 AISC-Seismic Provisions and the forthcoming International Building Code (IBC) 2000. ANALYTICAL MODELING TOOLS DYNAMIX – a program for the DYNamic Analysis of MIXed (steel-concrete) structures has been developed through this and previous research with capabilities to perform inelastic static and dynamic analyses of three- dimensional steel and RCS frames (El-Tawil et al. 1996a). Employing a bounding surface stress-resultant plasticity model, inelastic section behavior (i.e., moment-curvature response captured through the bounding surface model) is integrated to simulate overall member response through a flexibility element formulation. The resulting element accounts for the interaction of axial loads and biaxial bending moments in steel, RC, and composite beam-columns, including the effects of spread-of-plasticity, geometric nonlinearities (P-∆ and P-δ),