Lateral-torsional structural response from free-field ground motion

Lateral-torsional responses of structures subjected to the action of both the free-field ground inputs and external forces and moments are investigated. By expanding the work of Scanlan [1], both lateral and torsional foundation inputs due to a travelling shear wave are derived from the free-field point motions. The free-field torsional motions are used as the basis of numerical studies. Responses for different soil stiffness and structural characteristics are studied, as well as different dynamic models. In one dynamic model, the effects of interaction between lateral inertial force and lateral foundation motion are considered. And in the second model, the structure is excited by the external torque and torsional inputs. Both models are coupled to an elastic half-space. Finally, torsional structural response caused by torsional inputs is compared with lateral response caused by lateral inputs to determine the significance of torsional excitation on the seismic response of building structures. Numerical results show that these torsional seismic loads may be as large or larger than those from lateral excitations.