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

Abstract

In this article, the enhancement of the seismic function in tall buildings with semi-rigid connections accompanied by the Chevron bracing system was studied. 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 tall semi-rigid steel frames in two 12-story and 15-story structures as representatives of tall buildings. 56 semi-rigid frames were analyzed under seven 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. 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.

Keywords

• semi-frames
• chevron braces
• zipper columns
• near-fault areas
• tall buildings