Introducing a Seismic Bracing System in order to improve Seismic Performance of Steel Frames

One way to reduce seismic force is to use knee bracing systems. In this method, the diagonal limbs of the brace are connected to the knee joint. The duty of the brace is to create stiffness and the duty of knee member is to create ductility like a yielding damper. In this method, some novel results are achieved by combining Y type bracing with the knee members. In this regard, three samples of the proposed frame were tested in the laboratory of structure based on the ATC24 loading protocol. The results show that this seismic system has a good performance in energy absorption and stability. At lower frame displacements, the knee element begins the absorb energy process faster. The use of a knee bracing system can be a good alternative to the brace system due to its ease of replacement. The behavior of the hysteresis (force-displacement) curves obtained from the experimental tests show good results in force balancing. Moreover, due to relatively lower initial stiffness and strength, the proposed frame will perform well in low-intensity earthquakes. It was observed that the failure mechanism of the structure has an acceptable ductility in the plastic part of the system. In addition, it was shown that by moving the middle node towards the corner of the frame and increasing the eccentricity of this point, the stiffness of the frame decreases and as a result, the natural vibration period and system displacement increases under constant load.