Torsional Effects on Transverse Lateral Load Resisting Systems

Abstract eng:
This study focuses on the evaluation of the seismic behavior of transverse lateral load resisting system when the longitudinal load resisting system is subjected to large torsional forces. Two prototype three-dimensional steel structures with three diaphragm types and two different horizontal layouts of the lateral load resisting system were investigated. The structures have symmetric or asymmetric braced frames in the longitudinal direction and moment frames in the transverse direction. Three models of floor diaphragm interactions were considered: a bare steel frame with rigid constraints (BF+R); a composite frame with rigid constraints (CF+R); and a composite frame (CF) without rigid constraints. The structures were subjected to nonlinear static and dynamic analyses under two cases of torsional eccentricity. Case Mta_1 represents the conventional accidental eccentricity. Case Mta_2 represents the consideration of the bi-axial effects from the two principal directions. The results indicated that (1) the transverse frames show higher strength demands for the asymmetric configuration; (2) the columns in the 1st story in the transverse frames show inelastic behavior for the asymmetric configuration; and (3) The asymmetric structures without rigid diaphragm constraints (CF) show the largest increment of both base shear and interstory drift when such structures include the effect of Mta_2.

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