Document Type : Research Article
Authors
1
M.Sc., Earthquake Engineering, Iran University of Science and Technology, Tehran
2
Associate Professor, School of Civil Eng., Iran University of Science and Technology, Tehran, Iran
3
Professor, School of Civil Eng., Iran University of Science and Technology, Tehran
4
Assistant Professor, Department of Civil Engineering, Tafresh University, 39518-79611 Tafresh, Iran
Abstract
In the engineering community, it is very important to study the seismic behavior and the different damage states of structures under far/near earthquakes, and safe design of structures is seemed necessary in the seismic active zones. Special truss moment frame (STMF), as a Lateral force resisting system, is similar to other common moment frames; But the difference is in the existence of truss beams instead of beams with solid sections. Since the depth of truss beams is usually greater, they have more stiffness and are more resistant against bending moments than other beams. As a result, they are suitable for long spans. To prevent the formation of plastic hinges in the columns, an area is determined in the middle of the truss beams, which is called a special segment. The role of the members in the special segment is to yield under lateral loads and prevent the creation and expansion of plastic hinges to other structural members. In other words, the special segment acts like a fuse and prevents the damage in other structural members. Therefore, this paper compares the seismic performance of special truss moment frames equipped with energy dissipation devices such as buckling restraint braces (BRBs), viscous dampers (VDs), and friction dampers (FDs) under near and far field earthquakes. In this regard, the desired structures have been implemented in OpenSEES software, considering the non-linear behavior of materials, and subjected to incremental dynamic analysis (IDA) considering seven far and seven near field earthquakes with peak ground accelerations of 0.1g to 1.5g with a fixed incremental step of 0.1g. In order to perform the nonlinear dynamic time history analysis, 4 ten-story models have been used, which differ in the implementation of their special segment. In this way, one of the cases has Vierendeel special segments (without braces or dampers) and in the rest of the cases, buckling restraint braces, viscous dampers and friction dampers were installed inside the special segments. For this purpose, dampers and braces are placed diagonally inside the special segments. The results of IDA indicate that the near field earthquakes have a more destructive effect on structures rather than far field earthquakes. Moreover, the structures equipped with viscous dampers have a greater ability to absorb and dissipate the earthquake energy than other investigated systems. In the following, the comparison of the fragility curves for the studied structures has shown that the probability of complete failure of the structure equipped with buckling restraint braces near field earthquakes is 13.33% more than far field earthquakes. This value is equal to 12.5% and 23.5%, considering the friction and viscous dampers, respectively. Furthermore, the fragility curves indicate that damages in the structures increase strongly in the partial range with small changes in acceleration; because this range of damage is dependent on the intensity of the earthquake and it occurs with small changes in the acceleration of the earthquake. The effect of viscous dampers in reducing the response of the structure at the moment of the earthquake pulse, in near-field earthquakes, is much higher than the friction dampers and buckling restraint braces.
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