Investigation of the effect of nonlinear behavior of superstructure on seismic performance of base-isolated structures

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Mirbod Ahmad Reza; TAJMIR RIAHI HOSSEIN; DAEI MARYAM

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Journal: Modares Civil Engineering journal Year:2018 | Volume:18 | Issue:4 Page(s): 289-303

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Title

Investigation of the effect of nonlinear behavior of superstructure on seismic performance of base-isolated structures

Author(s)

Mirbod Ahmad Reza | TAJMIR RIAHI HOSSEIN | DAEI MARYAM | Issue Writer Certificate

Keywords

Base-isolation systemQ1

SuperstructureQ1

Nonlinear behaviorQ1

Ductility DemandQ1

Abstract

In the design of seismically base-isolated structures, it is expected that the isolator will experience Nonlinear behavior while the Superstructure still behaves linearly. Therefore for modeling these systems, a linear behavior is assumed for Superstructure and different nonlinear models are used for isolator. In seismic codes; strength reduction factor has been considered relatively small for base-isolated structures which put the seismic structural response in elastic area. But there are special conditions such as strong ground motions in which Superstructure behave nonlinearly. In this study, the Nonlinear behavior of seismically base-isolated structures is more accurately investigated. This is done using nonlinear time history analysis of structures using ground motions. Two sets of ground motions are selected which represent earthquakes with 475 and 2475 years return period The ground motion records have been scaled so that those are matched to NEHRP1997. OpenSees and Matlab softwares are used for modeling these structures. Among the most applicable parameters of the structural response is drift of stories. However, since ductility in shear frames is frequently used as a damage index, in the present study, the ductility of the stories was selected as the damage index of the structure. Therefore, the ductility 𝜇 which is defined as the ratio of the maximum deformation of the structure in the non-linear situation to the displacement of the yield point. The effective parameters on the response of seismically base isolated structure which are investigated are: response modification factor of the Superstructure, stiffness of the isolator, damping ratio of the isolator, stiffness of the Superstructure and damping ratio of the Superstructure. Studies of this paper are divided into two parts. In the first part, two-degree freedom model with viscoelastic isolator has been used to investigate the effect of Superstructure nonlinearity. Also a sensitivity analysis is done to find important parameters which have more effects on the systems response. Results of this part show that, Nonlinear behavior of Superstructure increases system Ductility Demand drastically. It is concluded that the period of isolator and Superstructure have the most effect on the Ductility Demand. In the second part, the effect of different parameters and higher mode effects on the response of seismically base-isolated structures is investigated using muti-degree of freedom models sited on isolator with bilinear behavior. Results obtained in this part also confirm the increase in the response of the system when the Superstructure has low strength. Likewise in this condition, the isolator deformation decreases. Distribution of Ductility Demand in the height of structure is also non-uniform in this condition and lower stories are more vulnerable. Isolators with a lower fundamental period and also isolators with a lower yield force lead to the least amount of isolator deformation and Ductility Demand of Superstructure. By increasing damping in the isolator, Ductility Demand of Superstructure will increase. A stiffer Superstructure with Nonlinear behavior has a much more Ductility Demand rather than similar structure which is more flexible. But when the Superstructure behaves linearly, the fundamental period of Superstructure and isolator deformation increase or decrease together.

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APA: Copy

Mirbod, Ahmad Reza, TAJMIR RIAHI, HOSSEIN, & DAEI, MARYAM. (2018). Investigation of the effect of nonlinear behavior of superstructure on seismic performance of base-isolated structures. MODARES CIVIL ENGINEERING JOURNAL, 18(4 ), 289-303. SID. https://sid.ir/paper/256630/en

Vancouver: Copy

Mirbod Ahmad Reza, TAJMIR RIAHI HOSSEIN, DAEI MARYAM. Investigation of the effect of nonlinear behavior of superstructure on seismic performance of base-isolated structures. MODARES CIVIL ENGINEERING JOURNAL[Internet]. 2018;18(4 ):289-303. Available from: https://sid.ir/paper/256630/en

IEEE: Copy

Ahmad Reza Mirbod, HOSSEIN TAJMIR RIAHI, and MARYAM DAEI, “Investigation of the effect of nonlinear behavior of superstructure on seismic performance of base-isolated structures,” MODARES CIVIL ENGINEERING JOURNAL, vol. 18, no. 4 , pp. 289–303, 2018, [Online]. Available: https://sid.ir/paper/256630/en

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