The role of phase difference components of ground motions in the torsional response of asymmetric buildings

It is demonstrated that the difference in phase content between orthogonal, horizontal, accelerograms can directly influence the effective (band-limited) torque energy applied to a plan asymmetric structure. This is not the case where a plan asymmetric structure is excited solely by a unidirectional, horizontal, accelerogram ground motion. It is shown that this effective torque energy is well correlated with building torsional (response) acceleration energy and element ductility demands for a broad class of multistorey structures. Nonlinear time-history analyses employing a database of accelerogram abstracted from USGS are used to quantify the influence of the phase difference content on these building responses. Bias in nonlinear time-history analyses based on a small sample of accelerograms caused by phase difference content is discussed.