Abstract

Over the last decades there has been a growing interest in the application of base isolation techniques for a number of structures such as buildings, bridges, nuclear reactors, data centers, etc. [1]. By means of the flexibility and energy absorption capability, the isolation system partially reflects and absorbs some of the input energy before this energy can be transmitted to the superstructure. The net effect is a reduction of energy dissipation demand on the structural system, resulting in an increase in its survivability. One of the difficulties in the application of isolation systems has been the explicit consideration of the non-linear behavior of the isolators during the design process. Another challenge has been the efficient prediction of the dynamic response under future ground motions considering their potential variability as well as the efficient control of competing objectives related to the protection of the superstructure and the minimization of the base displacement. In addition, the explicit consideration of the superstructure and the isolation system during the design process is another major difficulty. The objective of this work is to introduce a general framework for the design of base-isolated systems that addresses the previous challenges. A probabilistic approach is adopted for considering the variability of future excitations [2]. Isolation systems composed by rubber bearings are used in the present study. The non-linear behavior of these devices is characterized by a biaxial hysteretic model which is calibrated with experimental data [3,4]. In this setting, reliability is quantified as the probability that the response quantities of interest will not exceed acceptable performance bounds within a particular reference period. Such probabilities are estimated by an advanced simulation technique [5]. The corresponding design strategy is formulated as a non-linear constrained minimization problem with reliability constraints. The reliability-based optimization problem is solved by a first-order scheme based on descent feasible directions [6]. The proposed reliability-based design of base-isolated systems is illustrated by an application that considers a large finite element model for the superstructure. Results show that the explicit consideration of the superstructure and the isolation system during the design process can be quite beneficial in terms of the cost and performance of the final design of the combined system.