Evaluation of seismic performance of steel frames with semi-rigid connections with zipper bracing system under near- fault earthquakes using Opensees

The present study investigated the improvement of the seismic performance in steel buildings with semi-rigid connections with the Chevron bracing system. The ductility of steel buildings with semi-rigid connections has been significantly increased compared to frames with pinned connections, but the structures placed in near-fault areas show different behavior due to the nature of near-fault earthquakes because of pulsed waves with long periods. Therefore, it is better to improve the seismic performance of such frames to prevent possible damages and failures. For this purpose, modeling Chevron bracing system was first done using Opensees software by adding zipper columns in the semi- rigid steel frames in three ۵-, ۸- and ۱۲-story structures as representatives of low-rise, medium-rise, and high-rise buildings, respectively. Next, ۸۴ frames were analyzed under seven semi-rigid near-fault records using dynamic non-linear time history analysis. The analysis of modeled frames was done for both pinned and ductile connections and the case of removing and adding the zipper column, and finally, the comparison was done on results in terms of control of relative displacement and maximum lateral story displacement. The results showed that the use of zipper columns in Chevron braces in the steel frames with pinned and semi-rigid connections controls both relative story displacement and maximum lateral story displacement, and this effect is more significant in frames with ductile connections. In other words, more ductility capacity and better dissipation of seismic forces in the near-fault areas for semi-rigid frames could lead to desirable seismic performance. The presence of zipper columns in Chevron braces has made an integrated frame performance in the entire height of the structure due to the transmission of unbalanced vertical forces induced in the braced spans while decreasing story displacements. In addition, it has improved the seismic behavior of semi-rigid steel frames.

کلیدواژه ها:

Semi-rigid frames ، Chevron bracing ، Zipper column ، Near-fault area