عنوان مقاله [English]
One of the effective methods to improve dynamic response of steel structures is using adjunct elements among which metal yielding dampers are the most common. The working mechanism of these dampers in the lateral load-resisting structural system is related to the fact that development of inelastic strains in metallic dampers as the fuse elements results in dissipating the earthquake input energy imparted to the structure in a major seismic event. On the other hand, the aim of implementation of such damping devices is to substantially reduce the seismic demand in main structural systems, such as beams and columns, and hence, these members remains essentially elastic. One of the types of metallic yielding dampers is Added Damping and Stiffness (ADAS) metal damper that is a series of X-shaped steel sheets, which can be efficient in dissipating seismic energy but have shown apparent weakness due to the buckling resulted from development of axial forces in the dampers.
The objective of the present paper is to investigate the characteristics of a Modified Added Damping and Stiffness (MADAS) damper to be used as a supplementary device to improve seismic performance of low- and mid-rise steel structures. In MADAS damper, X-shape plates are configured in a way that their displacement along vertical axis is quite free, and hence, no axial force is developed in such metallic dampers. In this paper, a numerical Finite Element (FE) model of MADAS damper was simulated in ABAQUS and used to compare the predicted numerical results to those of experimental results of the MADAS damper subjected to cyclic displacements. It should be noted that, the experimental cyclic tests have been conducted by previous researchers for MADAS dampers, and, have shown superior cyclic performance compared to conventional metallic dampers such as Triangular Added Damping and Stiffness (TADAS) dampers.
In addition, three 4-, 5-, and 6-story buildings with steel moment-resisting frames have been studied, as the representative of the low- and mid-rise structures. For each building, two design alternatives, one for the case of conventional Steel Moment-Resisting Frame (MRF) and the other alternative is the one equipped with MADAS dampers, have been designed to be studied using numerical models. The structural members of the adopted buildings equipped with metallic MADAS dampers are designed according to ASCE/SEI 7-10 design code. The behavior of the numerical models has been investigated regarding seismic parameters including the Response Modification Factor, R, and Overstrength Factor, (Ω). The application of metallic dampers have shown to provide an increase of about (50%-80%) in the Response Modification Factor, R, and about (10%-20%) in the Overstrength Factor, (Ω). Pushover analyses for the numerical models have been conducted to obtain Base shear-Displacement curves. Based on the obtained pushover results, a maximum decrease of about 20% was noticed in the inter-story drifts of the numerical models in the Collapse Prevention (CP) performance level.
In addition, to investigate the seismic performance of analysis cases, time-history analyses of the numerical models subjected to 1940 El-Centro, 1994 Northridge, and 1978 Tabas earthquakes have been conducted. The earthquake records have been scaled to Maximum Credible Earthquake (MCE) and Design Based Earthquake (DBE) intensity levels.
Based on the obtained time-history results, a decrease of about (40%-50%) has been observed in the peak inter-story drift values due to the application of metallic MADAS dampers compared to that of moment-resisting steel frames. In addition, regarding the results of time-history analyses, the values of equivalent damping has been observed to be in the range of about (15%-20%) for the analysis cases. The obtained results indicate significant improvement in the seismic response of the structures equipped with MADAS dampers compared to the same buildings utilizing Steel Moment-Resisting Frames (MRFs) as their lateral-resistant structural system.