Equivalent viscous damping for buckling-restrained braced RC frame structures

While the direct displacement-based design (DDBD) method is commonly developed in seismic design of the single frame and is extensively discussed in the technical literature devoted to this subject, the proper evaluation of this method for dual frames system has received relatively little attention. Considering excellent hysteretic behavior, buckling-restrained braces (BRBs) have been increasingly configured in reinforced concrete (RC) frame to develop the reinforced concrete buckling‐restrained braced (RC-BRB) dual system. The RC-BRB dual frame system is a new lateral-load resisting dual system aimed to minimize the time and costs of repairs after an earthquake. The one of main parameters of the DDBD method is equivalent viscous damping (EVD) proposed to represent the energy dissipation of the system due to its inelastic behavior assumption. Since in the literature no damping equation has been given for the RC-BRB dual frame, the present study aims to provide a reliable EVD equation for the RC-BRB dual system, as well as in the values of the equation verified against real earthquakes, by conducting the nonlinear time-history analysis (NTHA). To this end, first, the numerical model was proposed and validated using the results of the available cyclic test in the literature. Then, the EVD equation of the RC-BRB frames was acquired based on a new method which calibrates the obtained EVDs through nonlinear time-history dynamic analysis of the structures under real earthquake records. The comparison between the calculated results and the corresponding ones acquired from previous equations illustrates that the proposed EVD equation is appropriate for estimating the energy dissipation of the RC-BRB dual frames. Furthermore, the results show that the EVD equations presented so far can conservatively estimate the damping level for the RC-BRB dual frame structures.