Seismic Design For Members Of Zipper Frames

Based on the conventional chevron braced steel frame system, an innovative structural system, so-called zipper frames, has been quickly developed in recent years, in which a vertical member(zipper strut) is added at the brace-to-beam intersections of chevron braced steel frames. Now, comparatively little research has been performed on the seismic behavior of the zipper frames and no reasonable and practicable design method was proposed in China. Based on the research work about the zipper frames, a new research work about the seismic design method for the structural members, including the brace, zipper strut, braced beam and braced column, was conducted in this dissertation. The specific research contents of this dissertation were as follows:1) According to the design method of suspended zipper frames, two numerical models, which the braces were respectively designed with and without considering the compression reduction factor ψ under cyclic load, were designed. Some indexes, including the natural periods, steel consumption and dynamic response under frequent and rare earthquakes, were analyzed and compared. By a comprehensive consideration of the steel consumption and dynamic response under earthquakes, the suggestion that the compression reduction factor ψ under cyclic load is not needed in the brace design has been put forward.2) A new design method of the zipper strut and braced column was proposed based on the SRSS combination rules and the braced beam were designed to resist part of the unbalanced force. Based on the above design methods, the structural models were designed and some indexes, including the natural periods, steel consumption and dynamic response under frequent and rare earthquakes, were analyzed and compared with those from the suspended zipper frame models. By a comprehensive consideration of the steel consumption and dynamic response under earthquakes, it is suggested that the zipper strut, braced column and braced beam should be designed according to the method proposed in this paper.3) In order to observe the fatigue damage of braces which were designed by the method proposed in this paper, a low cycle fatigue life estimation method based on the number of cycles of brace was used to compute the fatigue damage of braces under rare earthquakes. After compared with the suspended zipper frame model, the results show that the fatigue damage of braces of the two models is little. Normally, the fatigue damage of braces is difficult to effect the structure.