Experimental study of seismic performance of base-isolated frames with U-shaped hysteretic energy-dissipating devices

This study experimentally investigates the seismic performance of base-isolated structures using shake table tests. The base isolating system used in this study consists of laminated rubber bearings and U-shaped hysteretic energy-dissipating devices called UH dampers below. UH dampers used for a base-isolated structure experience significantly large deformations in both lateral directions when subjected to severe ground shaking. In order to accommodate such large deformations without noticeable strength degradation, UH dampers have been made of high toughness steel (HTS) that possesses excellent material properties compared to ordinary structural steel (SS). Based on preliminary finite element analyses, UH dampers employing slotted-hole details to induce uniform stress distribution are proposed. Also, the analyses of UH dampers with slotted-hole details suggests that they could be made of SS instead of relatively expensive HTS. Prior to the shake table tests, component cyclic tests of a laminated rubber bearing and the proposed UH dampers made of HTS and SS were performed to determine their structural characteristics. Base-isolated structures for shake table tests were initially designed based on the component test results and the equivalent lateral force procedure. Three shake table test specimens (a fixed-base structure, a base-isolated structure with UH dampers made of HTS (UH-H dampers), and base-isolated structure with slotted UH dampers made of SS (UH-S dampers)) were prepared. The shake table tests were performed with historical earthquake records. The shake table test results show that the base-isolated specimens with UH dampers achieved better seismic response compared to the fixed-base frame. In addition, the UH-S dampers present a seismic response that is comparable to the UH-H damper.