Abstract
<p>In this study, the function and application of seismic isolation system through lead rubber bearing isolator (LRB) in near-fault earthquakes are compared with fixed-base structures. As a result of their high frequency content, near-fault earthquakes impose huge energy on structures and cause severe damages. One of the appropriate solutions for this issue is the use of LRB which 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 the vertical component of earthquakes. To this purpose, we limit the displacements due to the horizontal movements of isolator through Gap spring which acts as a retaining wall and prevent shocks to other buildings. Moreover, this approach decreases the vertical movements of isolators and indirectly improves their behavior. In the current study, three buildings with four, eight, and 12 floors (with and without gap spring) were included. Isolators were manually designed in accordance with AASHTO-LRB regulations and the behaviors of both isolators and buildings are considered non-linear. Then we analyzed and compared the amount of energy, displacement, and acceleration of structure at the center of roof. The results indicated a significant decrease in the results of base shear, the acceleration of roof center, floors drift and energy imposed on the structure in the isolated system in comparison with the fixed-base structure.</p>
Highlights
The seismic isolation method includes isolation of the whole structure or a part of it from ground or other parts of the structure to reduce its seismic response during an earthquake
As figure 8 indicates, the amount of base shear decrease in isolated structures with a gap element is significant compared with fixed-base structures
Compared with non-isolated buildings, in the structures isolated by plastic seismic isolator of lead core, the amount of dissipated energy in bigger earthquakes is more than smaller earthquakes
Summary
The seismic isolation method includes isolation of the whole structure or a part of it from ground or other parts of the structure to reduce its seismic response during an earthquake. The main advantage of seismic isolation system is increasing the period of main frequency to transform it from frequency of a fixed-base structure and dominant frequency time of earthquake to higher one. Another advantage of seismic isolation is dissipation of imposed energy on the structure which leads to reduction of transformed acceleration to upper structure during an earthquake To hinder displacements originated from horizontal movements and shocks to adjoining buildings, a retaining wall was used For this purpose, buildings were designed with 4, 8 and 12 floors, a lateral load-bearing system of steel special moment frame according to ACIS360-05, the consideration of Peffects and the seimic regulations of 2800. The three models were analyzed once as a fixed-base and as an isolated structure without a gap spring; and the results were compared at the end (Ministry of Roads and City Planning and National Building Regulations Office, 2013; The Research Center of Housing and Urban Development, 2008)
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