Evaluation of Seismic Demand of Post-Tensioned Steel Moment Resisting Frames by Change in Post-Tensioned Effect Parameters

After northridge earthquake in 1994, different details for constructing new moment resisting connections to attain a ductile behavior under earthquake excitations were recommended. As a substitution instead of welded moment resisting connections, researchers recommended the utilization of post-tensioned moment connections in moment resisting frames to resist against earthquake loading. Post-tensioned connections are composed of high-strength steel cables which are erected parallel to the beam web and then are crossed through the column and finally would be fixed at the column’s flange face. Firstly, steel cables create compression between beam and column flanges, secondly they provide the resisting moment of connections against applied service loads and eventually these cables would cause self-centering of columns, which means that the columns would get back to their initial position after they are tilted by earthquake excitation. Moreover, two steel angle sections are added at the top and bottom surfaces of these connections, in order to dissipate the earthquake energy in the joint area. In this paper, in addition to introduction of this Connections, the modeling mode for them with the OPENSEES software and evaluation of accuracy of modeling results compared with experimental results, evaluated the Seismic demand of Post-Tensioned Steel Moment Resisting Frames by change in Post-Tensioned effect parameters for 4,7 and 10 story under time history dynamic analysis. The results indicate that reduced frames seismic demand with increasing force and the number of Post-Tensioned cables, thickness of angles and decreasing the ratio of length to thickness of angles.