Comparison of the behavior of isolated structures mounted on different types of friction isolators subjected to near-field earthquakes

Different solutions have been proposed by researchers in order to prevent the breakdown in welded connections between beam flange and column web, using moment connections. The use of post tensioned connections is one of the proposed solutions to reduce the damage in steel moment frame connections. The connection is used for high-resistant steel cables, which are in parallel with the beam flange and pass through the column and are anchored in the outer side of the column flange. The post tensioned force of steel cables causes the beam flange to be compressed against the column flange, which results in a connection resistance moment against the exploited loads. The resistance moment creates a restoring force that maintains the self-centering behavior of the frame. On the other hand, sequential earthquakes can cause damage to the steel structures, which has been investigated by some researchers. Residual relative displacement of the floors caused by the initial vibration of the structures, increases the vulnerability of the structure to the future earthquakes. Therefore, the reduction of this parameter improves the behavior of the structure against seismic sequence. In this study, the performance of five-, eight- and twelve-story frames has been evaluated in two cases of flexural rigid welded-connections and post tensioned connections under the influence of sequential records away from the fault. The results show that the maximum residual relative displacements of floors in the frames with post tensioned connection were reduced by about forty percent compared to frames with simple moment connections. Due to the decrease in the residual relative displacement of the floors in the said structures, the use of a post tensioned connection has led to the improvement of seismic behavior in comparison with moment frames with rigid welded connections against seismic sequence