Proportionate Dynamically Non-separable Buildings: A Class of Buildings With Horizontal Setback

This paper shows the existence of a class of horizontal setback buildings that exhibits (i) existence of two distinct types of mode, e.g., rigid floor mode and flexible floor mode, (ii) zero participation of flexible floor modes under spatially uniform ground motion, and (iii) zero participation of torsional modes. Such a class of buildings is referred herein as proportionate dynamically non-separable (PDNS) buildings. PDNS class differs from the existing concept of dynamically separable building in two respects. First, PDNS class does not impose any condition over the floor properties. Second, the eigen properties of the frames along one orthogonal direction may be different from that along other orthogonal directions. Therefore, PDNS class provides a wider latitude in modeling a building so as to minimize the effect of in-plane flexibility of the floor diaphragm. The existence of such buildings is shown in the form of horizontal setback buildings with all the wings oriented along the orthogonal directions (e.g., L, T, and + shapes).