Cyclic Behavior Assessment of Steel Bar Hysteretic Dampers Using Multiple Nonlinear Regression Approach

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Isolators prevent the transfer of earthquake energy to the structure and reduce its relative displacement by increasing the time period of the structure. Most isolators have low damping and hence, in some cases, the auxiliary dampers can play an important role in the increased damping and reduced displacement of the isolation system. In this paper, a new type of steel bar hysteretic dampers (SBHDs) as the auxiliary damper was studied and evaluated in the isolation systems. For this purpose, 1650 numerical models of SBHDs were constructed based on a laboratory sample with the bars of different length, number, and cross section. Also, the role of each of these geometric parameters in the seismic behavior of the dampers was evaluated using the hysteresis curves and the corresponding ideal bilinear curves. Owing to the deficiency of the analytical solutions in the estimation of the nonlinear behavior of SBHDs and to increase their accuracy, some models were proposed using the multiple nonlinear regression (MNLR) methods. The proposed relations can be used to obtain the displacements and the forces corresponding to the first yield point and the ultimate point, ductility ratio, elastic stiffness, post-yield stiffness, effective stiffness, and dissipated energy. The results showed that the proposed equations are able to estimate the cyclic behavior of SBHDs with the proper accuracy and well consistency, and can be used with full confidence.