Generalized Interstory Drift Spectrum

The recently developed drift spectrum is extended to buildings that do not deform laterally like pure shear beams. Similarly to Iwan’s drift spectrum, the proposed generalized interstory drift spectrum uses a continuous linear-elastic model to obtain estimates of interstory drift demands in buildings. However, the generalized interstory drift spectrum is based on a continuous model that consists of a combination of a flexural beam and a shear beam, rather than only a shear beam. By modifying one parameter the model used in the proposed generalized interstory drift spectrum can consider lateral deformations varying from those of a flexural beam to those of a shear beam. Hence, it permits us to account for a wide range of modes of deformation that represent more closely those of multistory buildings. The proposed generalized interstory drift spectrum is based on modal analysis techniques that are familiar to structural engineers and uses a damping model that avoids the problems that can occur in the drift spectrum. The generalized interstory drift spectrum is illustrated with various recorded ground motions. The effects of damping, higher modes, and lateral stiffness ratio are investigated and discussed. DOI: 10.1061/ ASCE 0733-9445 2006 132:6 840 CE Database subject headings: Drift; Approximation methods; Buildings, multistory; Building design; Beams.