Seismic Collapse Assessment of Low-Ductility Concentrically-Braced Frame Systems

Abstract eng:
Low-ductility steel concentrically-braced frame (CBF) systems that do not have seismic detailing or capacity design requirements are used extensively in moderate seismic regions of the United States. Structural behavior following brittle limit states is heavily dependent on secondary strength and stiffness, called reserve capacity. Recent full-scale cyclic tests and numerical simulations of low-ductility CBFs demonstrated potential sequences of damage and characteristics of reserve capacity for various system configurations. In addition, full-scale angle component and connection tests and corresponding numerical simulations have established a rigorous framework for modeling angle connections, which are very common in braced and gravity frame connections. With these full-scale component, connection and frame tests as the basis, seismic performance assessment of low-ductility CBFs has been conducted. This study considers a set of archetype buildings that represents common cases for the eastern and central US. Nonlinear response history analysis for ground motions scaled across a range of intensities is used to evaluate collapse potential of existing designs and to study enhanced design procedures that improve seismic stability. Selected results from this study are discussed in the present paper.

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