Abstract
This paper proposes a base isolating system to reduce the seismic demands of low- or medium-rise structures and experimentally investigates its seismic response using shake-table tests. The base isolating system considered in this study consists of laminated-rubber bearings and U-shaped hysteretic (UH) dampers which are made of high toughness steel (HTS) and are machined with slotted holes to increase their deformation capacities. A base isolated 2-story specimen for shake-table tests was first designed and cyclic tests of laminated-rubber bearings and UH dampers implemented in the base isolating systems were then carried out. The component test for the laminated-rubber bearings shows typically low lateral stiffness with enough vertical stiffness to carry gravity loads. The test results for the UH dampers demonstrate that the use of HTS material and the introduction of the slotted holes details increase deformation capacities by inducing uniform stress distribution along a UH damper. Finally, shake-table tests were performed using specimens shaken with increasing ground acceleration records. The shake-table tests show that the proposed base isolating system with UH dampers limits the seismic demands of a base isolated structure by lengthening its structural period, concentrating displacement demands on the base isolating floor and adding seismic energy dissipation from the UH dampers.
1. Introduction
Current seismic design philosophy intends that ordinary structures remain within an elastic range or experience minor structural damages under frequent earthquakes with a probability of exceedence of 50% in 50 years while allowing them to suffer major structural damages under a design-based earthquake with a probability of exceedence of 10% in 50 years (SEAOC, 1995; BSSC, 1997; ASCE, 2000; BSSC, 2003). However, this is contrary to the public’s expectation that structures engineered according to current seismic codes be in function immediately after a design-based earthquake. Socio-economic developments have significantly raised the required performance level of structures and seismic risk defined as loss of life and economic loss in urban areas has also increased because of the dense urbanization that has taken place worldwide.
4. Conclusion
This paper proposes a base isolating system to reduce the seismic demands of a low- or medium- rise structure and experimentally investigates the seismic response of the base isolated structure throughout shake-table tests after designing it according to energy balance seismic design procedure. The base isolating system considered in this study consists of laminated-rubber bearings and Ushaped hysteretic (UH) dampers which are made of high toughness steel (HTS) and are machined with slotted holes to increase their deformation capacity.
