Dynamics of a Class of Horizontal Setback Buildings with Flexible Floor Diaphragm

Abstract

This technical note presents a convenient modeling/design procedure for a class horizontal setback building to minimize the adverse effect of in-plane floor flexibility. Existence of such a class requires proportional eigenvalue problems of all the constituting frames regardless of the floor properties. For L, T, + etc. shape of buildings, the eigenvalue problem (of the frames) along two orthogonal directions need not be proportional. Moreover, the presence of a nonrectangular joint region theoretically precludes the existence of such a class. A step-by-step proportioning procedure, in the presence of a nonrectangular joint region, is outlined such that (1) “nearly” rigid floor modes exist, and (2) participation of the flexible floor modes under spatially uniform ground motion is close to zero.