Response of sliding structures to bi-directional excitation

Abstract Dynamic response of structures supported on the sliding systems to bi-directional (i.e., two horizontal components) earthquake and harmonic ground motion is investigated. The superstructure is assumed to be rigid and the frictional forces mobilized at the interface of sliding system are assumed to have the ideal Coulomb-friction characteristics. Coupled differential equations of motion of the structure with sliding system in two orthogonal horizontal directions are solved in the incremental form using Newmark's method with iterations. The iterations are required due to dependence of the frictional forces on the response of the system. The response of the system with bi-directional interaction is compared with those without interaction (i.e., two-dimensional idealization in two directions) in order to investigate the effects of bi-directional interaction of frictional forces. These effects are investigated under important parametric variations. The important parameters considered include the isolator properties (i.e., period, damping and friction coefficient) and the characteristics of the harmonic excitation (namely excitation frequency, amplitude ratio and phase difference). It is shown that if the effects of bi-directional interaction of frictional forces are neglected then the sliding base displacements will be underestimated which can be crucial from the design point of view. Further, the bi-directional interaction effects are found to be more severe for the sliding systems without restoring force in comparison with the systems with restoring force.