Torsion of a base-isolated building subjected to rotational components of earthquakes

This research focuses on seismically isolated buildings, specifically, the influence of the rotational components of seismic ground motion on the buildings' torsional response. Current approaches to ensuring the earthquake resistance of buildings and structures using seismic isolation are usually based on analyzing the impact of only the translational components of ground motion. The authors hypothesize that the rotational components of seismic action may, in certain cases, significantly affect a structure’s dynamic response. The primary research method involves conducting numerical experiments. The rotational component of seismic motion was simulated using a synthetic accelerogram generated according to Newmark’s model from two translational components of seismic motion. Two mathematical models are developed: a three-degree-of-freedom model for buildings supported on lead rubber bearings and a four-degree-of-freedom model for structures located on pendulum bearings equipped with plastic dampers. Analysis reveals that seismic rotations, particularly on soft soils, significantly amplify torsional effects. The accelerations at the corner points of the superstructure can increase significantly: up to 4 times for lead rubber bearings and up to 3 times for pendulum bearings compared to the accelerations at the center of mass. Furthermore, displacements in the corner isolators exceed the center of mass displacement by up to 16% for lead rubber bearings and up to 5 times for pendulum systems. Between the two considered seismic isolation systems (elastomeric and pendulum isolators), the rotational components of seismic action exert the greatest effect on the dynamic response of a building isolated by pendulum bearings. This circumstance should be taken into account when designing buildings with a seismic isolation system exhibiting low torsional stiffness.