Design Seismic Accelerations in Buildings

A procedure is presented for determining the design distribution of story shears and overturning moments in buildings subjected to strong ground motions, with particular emphasis on tall buildings. A parameter study was conducted and modal analyses were performed to determine the influence of the following variables on the most probable response to earthquake excitation at various levels in a building: (1) The type of structural behavior, ranging from that of a purely flexural beam to that of a purely shear beam; (2) the fundamental frequency relative to the intersection of the linear branches of the response spectrum; (3) the degree of structural setback, ranging from uniform to setback over 80% of the height; and (4) the degree of foundation compliance. For all parametric combinations a bilinear response spectrum was used and the secondary P-Δeffects were incorporated into the modal analysis.