Document Type : Article
Authors
1
Dept. of Civil Engineering Islamic Azad Universi&zw
2
Dept. of Civil Engineering Sharif University of Te&
Abstract
The response reduction factor (R) is employed in different seismic design and analysis codes to reduce the level of design forces and utilize the existing capacity of structures in dissipating the seismic input energy caused by the nonlinear behavior of structural systems. Different parameters are involved in finding this factor, among which the ductility related reduction factor, ($R{mu}$), the overstrength related reduction factor, ($Omega_0$), the redundancy related reduction factor, ($R_r$), and etc., could be named. On the other hand, application of energy dissipation systems, especially added dampers, has gradually become an essential part of the seismic design of structures. The design guidelines of buildings equipped with these devices have already been provided in a number of seismic design codes, such as ASCE7-05. In this paper, a so-called Response Reduction Factor is introduced to take into account the effect of added viscoelastic dampers in dissipating input seismic energy in special steel moment resisting frames, ($R_xi$). In that regard, a number of 2-D SSMRF models, with a different number of bays and floors, are selected. The viscoelastic dampers are uniformly distributed along the height of the structural models, employing a Kelvin arrangement, in their mathematical modeling. Nonlinear static analyses (pushover analyses) are used to determine the added damping related response reduction factor, ($R_xi$), for these structural models. Nonlinear dynamic time history analyses are performed to investigate the obtained results using seven far-field earthquake components recorded on soil type C (dominant period of 0.4 to 0.7 second), based on the ASCE7-05 code. The results show an increase in the ductility related reduction factor, ({$R_mu$}), as well as the overstrength reduction factor, ($Omega_0$), by increasing damping ratios of structural systems caused by added viscoelastic dampers. Also, on average, the response reduction factor, ($R_xi$), is determined to be equal to 1.09, 1.15 and 1.28 for added damping ratios of structural systems equal to 5%, 10%, and 15%, respectively. The OpenSees program is used for numerical analyses.
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