Base isolator with variable stiffness and damping: design, experimental testing and modelling

Vulnerability in base isolation system of civil structures originated from passive nature of the rubber material raises the urgency of developing smart base isolation system with adaptive and controllable properties, i.e. variable stiffness and damping. To address this issue, this paper presents comprehensive investigations on a novel adaptive base isolator, including design, experimental testing and dynamic modelling. Smart rubber with field-dependent modulus and damping property is incorporated into the laminated base isolator design. Experimental testing is conducted utilising an advanced shake table facility to examine its performance under cycling loading. Results show that the adaptive base isolator possesses a stiffness increase of more than 16 times and damping ratio between 10% and 27%. With such features, it can be developed into a smart base isolation system to protect civil structures against any type of earthquake. Results also show that this device has high nonlinear hysteresis, i.e. shear stiffening behaviour. A mechanical model is thus required to describe the complex behaviour of new adaptive base isolator. A new strain stiffening element is proposed for this purpose. Comparison between the model and the experimental data verifies the fidelity and effectiveness of the proposed model.