Essential Facility Benefits from New Base Isolation Technology

Abstract

A common problem that is encountered in the design of low-rise base-isolated buildings is the resistance to uplift. Rubber isolators have low tension stiffness and strength and traditional spherical friction pendulum (FP) isolators operate based on contact and thus, have no tension resistance. As a result, most base-isolated buildings require a substantial number of braced frames bays to limit tension demands on the isolators. An innovative new tension-restraint FP isolator has been developed that allows tension and shear to be transferred through the isolator simultaneously. This paper describes the design of an 82,000 square-foot 2-story essential facility that utilizes both tension-restraint FP isolators and traditional spherical FP isolators. A performance-based design approach was utilized for this project in order to satisfy the enhanced seismic performance objectives dictated by the nature of the mission critical functions served by the building. A three-dimensional computer model of the building was developed utilizing nonlinear elements for the FP isolators. Time history analyses were performed using seven sets of ground motion records for each level of seismic hazard and the sensitivity of the building response to several modeling parameters was investigated. The use of the tension-restraint FP isolators was beneficial to the project because it minimized the number of the braces required in the superstructure and thus provided a cost-effective means for meeting the seismic performance objectives of the essential facility. The reduction in braces also afforded considerable architectural flexibility and minimized the impact on the functional layout of the building.