Inelastic Behavior of Asymmetric Multistory Buildings

Studied in this paper is the inelastic seismic behavior and design of asymmetric multistory buildings emphasizing, primarily, the use of story shear and torque histories. The following six different structural characteristics and their effect on the torsional response of buildings are analyzed: strength of orthogonal resisting planes, stiffness asymmetry, strength asymmetry, planwise distribution of strength, number of resisting planes, and intensity of the ground motion component in the orthogonal direction. As a result of these analyses several techniques and conceptual guidelines are developed to correct the planwise unbalance in deformation demands typical of asymmetric structures. The two most important are to increase the torsional capacity of the system by introducing resisting planes in the orthogonal direction, and to modify the stiffness and strength distribution to localize yielding in selected resisting planes. Using these guidelines the undesirable earthquake response of a very asymmetrical building is effectively corrected by changing slightly the strength of a few key resisting planes. Finally, it is concluded that the use of the story shear and response histories in conjunction with the corresponding story yield surfaces is a powerful tool for conceptual understanding of the earthquake behavior of asymmetric structures.