Development, Experimentation, and Implementation of a Gap Damper System to Limit Displacements in Extreme Ground Motions

Abstract

Studies have shown the effectiveness of providing supplemental energy dissipation in base-isolated structures to reduce displacements at the isolation level, often with consequences to superstructure performance. A previous analytical study demonstrated the benefits of providing this energy dissipation at a specified gap larger than the design displacement. The gap before engagement allows the base isolation system to meet performance criteria in varying levels of ground excitation. Use of this ‘gap damper’ device eliminates undesirable effects often exhibited with large amounts of supplemental damping at lower intensity motions. Using and expanding upon results from an analytical study, the primary purpose of this research was to develop devices for practical implementation. Development of the devices demanded simplicity, feasibility, economy, and reliability to be an effective option in building design and construction. Multiple designs were proposed, and a final design was chosen based on selection criteria and finite element analyses. The device was designed and tested in Auburn University’s Structural Research Lab. Experimental results were compared with theoretical model results to verify behavior and make necessary adjustments for design of a shake table experiment at the University of Nevada-Reno’s Earthquake Engineering Lab. In addition, results were calibrated with detailed finite element analyses to investigate system behavior that could not be achieved in the lab testing environment. With demonstrated benefits from analytical and experimental testing, a detailed design procedure was developed for practical implementation of a gap damper system. Using the design procedure, a case study building was analyzed in OpenSees and SAP2000 for a comparison basis and demonstration of practical modeling techniques. The results of the case study clearly show the reduction of displacements at the isolation level with some consequences in the superstructure for extreme ground motions. Overall, the gap damper system shows promise in providing a performance-based system that can effectively reduce isolation level displacements without affecting response in low-to-moderate level intensity motions.