Base isolation for torsion reduction in asymmetric structures under earthquake loading

Abstract

This paper examines the effectiveness of a bilinear hysteretic base isolation system in lowering the shear forces and torques generated in a structure by two‐way, translatory ground motions. The study is restricted to single‐storey, three‐dimensional structures having asymmetries in both horizontal directions and being excited by the El Centro (May 1940) earthquake motions.It is shown that with base isolation the structural torques are drastically reduced, even if the structural eccentricity is large. This reduction in structural torque is greatest when the isolation system's centre of stiffness coincides with the structure's centre of mass. The highly dissipative action of the isolation system provides strong modal decoupling which prevents the translational motions from resonantly driving the torsional motions. The maximum base displacements, due to both translation and rotation combined are less than 11 cm, which is well within the limits of currently available isolation system components.The dynamic action of the base isolation system is outlined and currently available isolation system components described.