Development of low-cost base isolation system for residential housing in high seismic zones

Base isolation is the most effective technique in reducing earthquake force transmitted to a building. Uncoupling a structure from earthquake effect is the main objective of using this device. The basic principal of base isolation system in reducing earthquake force is by lengthening the structure period far away from the high earthquake force period range. Therefore, the seismic demand on a structure and earthquake force transferred to a building are decreasing significantly. Generally, base isolation consists of alternating horizontal layers of rubber and reinforcement. The reinforcement serves primarily to prevent bulging effect of rubber layers under compression load. The restrain of rubber enhances the vertical stiffness of isolators due to the near-incompressibility of the rubber, resulting in a vertical stiffness that is significantly greater than the horizontal stiffness. Currently, seismic isolation technology is applied across the world on large and expensive buildings. It is necessary to reduce the weight and cost of isolators to extend this effective yet expensive earthquake-resistant strategy to housing and commercial buildings. The isolators used in these applications are large, heavy and very expensive. A single isolator can weigh one ton or more. The primary weight in an isolator is caused by the reinforcing steel plate employed to provide the vertical stiffness of the rubber-steel composite element. In order to develop low-cost base isolation, the weight and cost of isolator must be reduced significantly. Therefore, the research purpose described in this report is to suggest that both cost and weight can be reduced by eliminating the steel reinforcing plate and replacing them with a perforated reinforcement. In this research project, the characteristics of perforated-reinforced elastomeric isolators (PREIs) were investigated. A series of experimental test and finite element analysis (FEA) were conducted to observe PREIs behavior under compression and lateral load. The rubber material employed in the experimental test is denoted as rubber-A. The vertical tests were conducted by testing 1 specimen. A specimen was monotonically loaded to a compressive force at zero horizontal displacement. Once the compressive load was achieved, it was fluctuated over three sinusoidal cycles and then monotonically unloaded. It was carried out to investigate PREIs vertical characteristics under compression load of 80 kN. BS EN 1337-3:2005 standard was utilized as the fundamental procedure for compression test. Furthermore, in order to observe the horizontal characteristics of PREIs, horizontal test was also performed by testing 1 specimen. The horizontal test was performed under horizontal displacement control. The specimen was tested under constant vertical load of 80 kN and moved freely in lateral using cyclic shear with three fully reversed cycles at four maximum strain levels of 5%, 10%, 20%, 50% and 100%. BS EN 15129-2009 standard was utilized as the fundamental procedure for lateral test. The finite element analysis was also carried out to estimate the behavior of isolator and used to observe the characteristic of isolator including stress and strain. Further analysis using FE was also conducted to observe the characteristic of modified circular perforated-reinforced elastomeric isolators (MC-PREIs) in order to derive the lower horizontal stiffness by modifying loaded area of PREIs. The experimental test and FE results indicate that producing a perforated-reinforced isolators as low-cost base isolation system for light structure is supposed to be possible. The isolators are specified as low damping natural rubber bearing since the damping ratio is below of 10%. The perforated-reinforced isolators significantly lighter and the cost will be extremely lower than conventional isolators. In addition, FE of modified circular perforated- reinforced elastomeric isolators (MC-PREIs) also indicate the possibility to reduce lateral stiffness of isolator significantly