RESPONSE MODIFICATION FACTOR OF SPECIAL STEEL TRUSS MOMENT FRAMES

In recent decades the use of special truss moment frames has been developed as relatively new steel frame systems in high seismic zones. These frames dissipate the seismic energy through the specific ductile parts that are located near the middle of the span of the truss beam. In this study the response modification factor of steel moment frames with specific truss beams due to the ductility and over strength was determined. The analysis was carried out using linear static analysis (pushover). In order to consider the nonlinear behavior of the material in formation of the plastic hinge، it was used the elasto-plastic behavior and it was assumed that the plastic hinge are created at the top and bottom of the column and beam. The analyses are carried out for two types of the frames، Vierendeel and across diagonals frames. These frames are evaluated for two cases، two and three spans، and also for different stories، 3 to 8-story. The results are shown that the response modification factor of the Vierendeel frame is more than the across diagonal frame’s and has a better seismic performance. The results also show that the response modification factor is dependent on the height of the structure، so that this factor is increased with increasing the height of the structure.