Non-Linear Seismic Response of Base-Isolated Frame Structures Using Rubber Bearings

Abstract

Over the past two decades, much progress has been made in research and application of the base isolation of structures as means of providing earthquake resistance to a structure. However, the trade-off between the extent of acceleration reduction and the response of a base-isolation system has not been given a serious consideration. This work uses a new material constitutive model for rubber bearing base-isolation system, which adopts the technique of real-time structural parameter modification. To achieve this, a finite element modeling and analysis are performed as a comparative study between a conventional totally fixed-base steel frame structure and similar base-isolated structures using rubber-steel bearings. The structures are subjected to the El-Centro, N-S earthquake. In order to include nonlinearity effects, a non-linear hyperviscoelastic material model has been used and linked to ABAQUS software as a user defined material subroutine (i.e., UMAT). Special connector elements are selected from ABAQUS library to connect the rubber bearings to the frame structure and the foundations in order to achieve the required kinematical constraints at the connection points. The model is validated by carrying out a comparative study of the results obtained from the analysis of the presented material model with those obtained by using the existing ABAQUS material models (e.g., Ogden material model). The results show a significance efficiency of using the rubber bearing isolation in order to uncouple the structure from the seismic ground motion. Moreover, it has been proved that the used material model is more effective to capture the behavior of the base-isolated structures expressing a notable reduction in acceleration and an increase in the structural resistance to earthquake excitations.