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ABS Poormasood

It is perceived as an important design issue to protect special structures to continue their service during earthquakes. Base isolation, as an effective technique, decreases seismic acceleration and forces induced in a structure by period elongation and increasing of damping. Production of widely-used lead-rubber base isolation devices (LRB's) needs specific technology, especially for making an adequate cohesive connection between rubber layers and shim plates, inserting the lead core and load test of the device. In an LRB, the lead core provides the initial lateral stiffness and the hysteretic damping afterwards, the rubber layers produce the restoration force, and the steel plates provide for the vertical stiffness.

In the present thesis, acknowledging the basic principles of a base isolation system, a new device, FSRB, is introduced that is both workable and economic. It is consisted of a central cylinder of rubber surrounded by external steel layers with end frictional contacts. Therefore, the need for consecutive rubber and steel layers is eliminated and the rubber and steel parts are completely separated. The peripheral steel plates provide the vertical stiffness and also the damping in lateral motion by friction. The proposed system is evaluated against the LRB both under vertical and lateral loading. It is shown to be an efficient system regarding vertical and lateral stiffnesses and the distribution of different components of stress in various parts of the device. It is concluded that the proposed device is an economic and safe alternative for the current base isolation systems.

Key words: Base isolation, LRB, FSRB, vertical stiffness, lateral stiffness.