Hide/Show Apps

A comparative study on the nonlinear behavior of chevron and suspended zipper braced steel frames

Download
2010
Özçelik, Ahmet Yiğit
Chevron braced steel frames require large beams to redistribute the unbalanced vertical forces exerted on the beams after brace buckling. A new frame configuration similar to chevron brace was proposed in literature, where zipper columns were attached between mid-spans of the beams from second to top story. During severe ground motion, the unbalanced vertical forces caused by buckling of lower story braces are in this case redistributed to the upper story braces by these zipper columns. Consequently, all story braces buckle successively from first to top story brace instead of concentration of inelastic action in one story. This system has been improved recently by adding an elastic hat truss between the top two stories to prevent formation of a full zipper mechanism and to prevent collapse. Two-phase numerical study is undertaken in this study to evaluate the response of chevron and suspended zipper braced frames, where the objective of the first phase is to observe the change in the performance of the configurations for different sets of initial imperfection and rotational spring stiffness values. Rotational springs are added at the end nodes of the braces to represent the effects of gusset plates and initial imperfection is assigned to the mid-length of the braces to achieve proper buckling behavior. The objective of the second phase is to compare the response of chevron and suspended zipper brace frames. For this purpose, three, nine and twenty-story buildings are designed for both brace configurations. The designed buildings are analyzed under static and dynamic loadings.