Response of sliding structures to earthquake support motion

To study the effectiveness of sliding supports in isolating structures from damaging earthquake ground motions, a mathematical model of a single degree of freedom structure supported on a sliding foundation and subjected to the N-S component of the El Centro 1940 earthquake is considered. Spectra for absolute accelerations, relative displacements, relative-to-ground displacements, sliding displacements and residual sliding displacements are evaluated for three mass ratios, four coefficients of friction and a damping of 5 per cent critical. It is observed that, for structures with periods less than 1-8 s, for the coefficients of friction considered, the suprema of relative-to-ground displacements, sliding displacements and residual sliding displacements are only of the order of 1–25 times the peak ground displacement. To study the response sensitivities, the spectra for absolute acceleration and sliding displacement of the 1949 Olympia earthquake (S86E component) are also presented. It is concluded that sliding supports can be quite effective in isolating structures from support excitations.