Study of the effect of energy absorbing element in seismic performance of steel frames with symmetric y-shape concentric bracings

One of the common bracing systems in our country is Y-shaped bracing system. Because of architectural advantages, it attracts more attention in comparison to x shape concentric braced frame (CBF). But, its stiffness is less and it has more potential for out of plane buckling. One of the extensively used methods for improving the seismic behavior of the structural systems is using the passive control systems. By reducing seismic demand and increasing ductility, this control way can reduce the rate of seismic damage. Yielding dampers are one of the elements to achieve this kind of control in the structures. Because of good ability of yielding dampers in earthquake energy dissipation, the use of these dampers is increased through recent decade in passive control of structures. Due to development of passive control methods for earthquake energy dissipation and for preventing the structures from earthquake losses, this paper proposes a new improved dissipating element for Y shape bracing systems which could be used for structural rehabilitation of steel structures. The basis of the proposed element operation is its operation as a fuse element to improve the bracing elements behavior. The operation of the proposed element is in such a way that before formation of a hinge in bracing element, the presented element is yielded and by absorbing appropriate energy, prevents the bracing elements from inappropriate performance. Before inserting the proposed element in the bracing frames, using the ANSYS software, the element performance is studied for different dimensions and appropriate dimensions are determined. The energy absorbing element is inserted into two different positions in the bracing systems of interest. 2D steel frames with three different number of stories (4, 6 and 8 story frames) are modeled in SAP 2000 software, using conventional braced frames and their behavior is compared to braced frames with the proposed energy absorbing element. The frames are analyzed through nonlinear time history analysis, using appropriate time history records from near source and far source locations. The results show the appropriate ductility of the proposed element, the improvement of bracing elements behavior and also, the higher energy dissipation of the new bracing system, which can be shown through comparison of the hysteresis loops of the bracing frames, solely and those with proposed elements. It could be shown that the ductility of the system is affected by the position of the proposed element. Reducing the base shear due to earthquake records and also decreasing the permanent displacement of the structural stories after earthquake occurrence are some of other advantageous of the presented element. Inserting the new proposed elements in bracing system can also reduce the input energy of the system, during the earthquake. In general view, it can be concluded that by appropriate design of the proposed element, the other structural elements behave elastically and the inelastic behavior is happened in the presented elements, which is resulted in improving the seismic structural performance of the new system.The results of this study can be used in seismic design of earthquake resistant structures