Abstract
Despite the growing applications of the performance-based design concepts for seismic design of structures, the response modification factors for structural systems proposed by the current design codes and standards do not generally consider different hazard and performance levels. Therefore, these factors are not directly applicable for performance-based design purposes. As a step to address this shortcoming, the present study aims to propose multilevel response modification factors for multistory dual moment-resisting frames equipped with eccentric braces and vertical links corresponding to different seismicity levels and performance targets. The concept of demand and capacity response modification factors is introduced, and these parameters are calculated for moment-resisting frame structures with 3-, 5-, and 7-stories before and after the addition of vertical steel shear links. It is shown that the calculated capacity response modification factors for the dual frames equipped with vertical links are generally higher than the demand response modification factors proposed by the design code for such systems under the design basis earthquake hazard level. This indicates the efficiency of the eccentric braces with the vertical links in improving the seismic reliability and performance of the moment-resisting steel frames. Based on the results of this study, the demand response modification factor for the studied dual lateral load-resisting system is calculated to be in the range of 7–10.
Highlights
As one of the efficient methods to improve the seismic performance of structures, shear link elements can be used to act as a seismic fuse and dissipate a part of the earthquake input energy through plastic deformations under shear and bending (Schmidt et al, 2004)
The choice of the response modification factors between the demand and the supply R-factors corresponding to a given performance level will guarantee that the frame performs at the considered performance level for the intensity corresponding to the given performance level or lower intensities
For the first time, a multilevel approach was used to derive the response modification factors of a dual structural system consisted of intermediate moment-resisting frames and eccentric bracing systems equipped with vertical links
Summary
As one of the efficient methods to improve the seismic performance of structures, shear link elements can be used to act as a seismic fuse and dissipate a part of the earthquake input energy through plastic deformations under shear and bending (Schmidt et al, 2004). Shayanfar et al (2014) studied the seismic performance of eccentrically braced frames equipped with vertical shear links using the performance-based plastic design concept. Lian and Su (2017) conducted an experimental program on eccentrically braced frame structures equipped with vertical shear links. Caprili et al (2018) performed a full-scale experimental program on a one-story eccentrically braced frame structure with horizontal and vertical shear links. Vetr et al (2017) and Vetr and Ghamari (2019) performed a wide range of experimental and analytical studies on the seismic behavior of eccentrically braced frames with vertical links. Mohsenian et al (2020a, 2021) proposed the application of the eccentric bracing system with vertical links for seismic retrofitting of moment-resisting steel frames. The results of the abovementioned studies have demonstrated the ability of shear links to control lateral displacements and provide high energy dissipation capacity under earthquake excitations
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