Torsional coupling in sliding base-isolated structures

The lateral-torsional response of base-isolated structures, with sliding isolation system due to bidirectional lateral ground motion, is studied. The objective of the study is to identify the key system parameters that lead to significant torsional coupling in sliding base-isolated structures. The analysis procedure adopted can capture the highly nonlinear behavior of sliding systems in plane motion. The nonlinear biaxial stick-slip characteristics of sliding bearings and the velocity dependence of coefficient of friction are accounted for. The study considers multistoried structures with variable number of bearings subjected to the effects of earthquakes with various frequency content and different peak ground accelerations. It is shown that, although the total superstructure response is reduced significantly due to the effects of sliding base isolation, torsional coupling can be significant depending on the superstructure eccentricity and the lateral-torsional flexibility of the superstructure and the base.