Estimating Inelastic Bi-Directional Seismic Response of Multi-Story Asymmetric Buildings Using a Set of Combination Rules

Abstract eng:
Time history response analysis on 3D parametric models of multi-story asymmetric-plan buildings with nonlinear behavior considering both Uni- and Bi-Directional earthquake actions are carried out. Two different 5 story building models formed by six, and seven resisting planes (frames) connected at each floor by a flat slab (rigid diaphragm) and fixed at the base. The plan has an aspect ratio 2:1, and in the center of mass (CM) three degrees of freedom (two horizontal displacements and the in-plan rotation) and lumped masses were considered. Structures with different characteristics were defined based on the typical elastic parameters, and the seismic response modification factor R*. The artificial earthquake action was applied in Uni- and Bi-Directional form, varying the angle of incidence α in 15º increments to find the critical angle where the overall and local responses are maximized. For the inelastic model it was considered that the yielding takes place in the end joints of each element and is generated by interaction of bending moments and axial forces. Overall and local maximum responses were studied. The ratios between the maximum responses considering Bi-Directional earthquake action and inelastic behavior, and the maximum response estimated by some combination rules (SRSS and 100/β, with β = 40, 60) considering elastic response and Uni-Directional earthquake actions in two perpendicular directions (α = 0°; 90°), were evaluated. The results show that this procedure provides reasonable estimates of the inelastic maximum responses. In addition, the translational and torsional displacements of the CM of each floor, as well as the vertical translational displacements (δ) and bi-axial rotations (φ and ϕ), were seen to be similar to the values obtained from elastic analysis amplified by the magnitude of the response modification factor R* used in the design.

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