Base Isolator Lead Rubber Bearing Technology In High Risk Seismic Zone

Lead Rubber Bearing (LRB) is a type of base isolators of anti seismic systems that has been widely used in the buildings to reduce the earthquake loading. This LRB comprises several layers of natural or synthetic rubbers that have critical damping ratios between 2 to 5 percent. To be able to resist the vertical loading (to avoid buckling), the rubber is inserted with a number of steel plates which are attached to the rubber layers by using a vulcanizing system. For the past few years, the design of base isolation, which is implemented to protect the buildings from the hazard and damage due to earthquake, has been used as a new technology in the design of buildings in high seismic zones. Several types of structures have been designed by this technology, either those had been designed or still under construction. This technology has been adopted in few countries, such as China, Korea, Indonesia, Japan, and USA.

In the structural modeling of a building with the base isolators, it is required to create an optimum base isolator model so that an accurate prediction on the lateral and vertical displacements can be achieved. The analysis is carried out using dynamic analysis on the following three structural types, i.e. high-rise (20 stories), medium-rise (12 stories), and low-rise buildings (8 stories). For buildings with base isolators, the accelerations due to the earthquake loadings are less than those in the conventional buildings. The seismic energy from the substructure (foundation) is reduced by the lead rubber bearing prior to be transmitted to the superstructure. To increase the damping ratio, a circular rod made of tin is provided in the center part of the bearing. From Structural Analysis Program analytical results, for buildings constructed in the high seismic regions on LRB base isolators provide better structural responses. Buildings with LRB have longer natural periods than the buildings stand on fixed bases. Besides, in terms of structural internal forces, the building on LRB is as if constructed in the lower risk seismic zones, because the seismic energy is reduced prior to be transmitted to the superstructure.