1ImprovingtheSeismic Behavior of Symmetrical Steel Structures under Near-Field EarthquakeUsing aBaseIsolation Method Lead Rubber Bearing Isolator

In this research, the function and application of seismic isolation system through lead rubber bearing isolator (LRB) in near-fault earthquakes have been studied compared with fixed-base structures. According to their high frequency content, near-fault earthquakes impose huge energy on structures and cause severe damages. One of the appropriate solutions for this problem isusing LRB which with a proper function decreases the amount of imposed energy on structures. To improve the function of isolated structures under the near-fault earthquakes, isolators are designed in a way to tolerate vertical component of earthquakes. In such conditions, we limit the displacements due to the horizontal movements of isolator through Gap spring which acts as a retaining wall and prevents shocks to other buildings. Moreover, this approach decreases the vertical movements of isolators; therefore, it is indirectly useful for improving isolators’ behavior in vertical direction. In this study, three buildings having four, eight, and 12 floors (with and without gap spring) with special moment frame each of them connected to a fixed-base once and another time connecting to a seismic isolating system have been considered. Isolators in this research were manually designed according to AASHTO-LRB regulations and the behaviors of both isolators and buildings have been considered non-linear. At the end, we analyzed and compared the amount of energy, displacement, and acceleration of structure at the roof center, and results indicated a significant decrease in the results of base shear, acceleration of roof center, floors drift and energy imposed on the structure in the isolated system compared with the fixed-base structure.

Keywords:

Lead rubber bearing isolator , near-fault earthquake , earthquake vertical component , gap spring , retaining wall , analysis of the non-linear time history