مهندسی عمران شریف (Feb 2019)
SEISMIC PERFORMANCE ASSESSMENT OF ISOLATED STEEL MOMENT FRAMES WITH LOSS APPROACH
Abstract
Earthquakes pose inevitable damage and loss of life in structures. Seismic isolation has proven to be an effective method to reduce the seismic vibration and mitigate seismic losses and damage costs. The isolator drastically reduces the main frequency of the structure and subsequently lowers the acceleration of the floors. While this flexible layer protects the building from destruction, it undergoes a relatively large displacement demand. Isolated structures as well as fixed structures could suffer from inelastic deformation and serious damage under intense seismic ground motions. Performance-based seismic design (PBSD) is a concept that permits the design of buildings with reliable understanding of the risk of life, occupancy, and economic loss that may occur as a result of future earthquakes. Also, Seismic loss estimation method combines seismic hazard, structural response, damage fragility, and damage consequences of allowing quantification of seismic risk based on seismic performance of a building is expressed as the probable damage and resulting consequences of a building's response to earthquake shaking. Nonlinear 4-story archetypes of conventional special moment resisting frame and isolated intermediate moment resisting frame were compared with each other under Far-Field and Near-Field ground motions. Detailed three-dimensional (3D) numerical models of the structures were developed in OpenSees software and Performance Assessment Calculation Tool (PACT) was used for the loss estimation of archetypes. The decision variables in this study were defined as expected annualized repair cost or financial losses (EAL) and expected annualized fatalities (EAF). The analysis results showed that seismic isolation reduces collapse probability, EAL and EAF in superstructures significantly and can be cost effective in mitigating seismic risk. Seismic isolation reduces EAL by 72\% and 67\% under Far-Field and Near-Field ground motions, respectively. Furthermore the result of this study showing that the effectivity of isolation system decreases in Near-Field compared with Far-Field ground motions. The economic feasibility studies showed that if isolation system is used, pay-back period times are around 14 and 18 years under Far-Field and Near-Field ground motions, respectively. The benefit of loss estimation approach is an improved method to assess the effectiveness of isolation system in terms of loss estimation.
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