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Evaluation of cyclic behaviour of special concentrically braced frames with built-up diagonal braces

ABSTRACT The built-up special concentrically braced frames (BSCBFs) containing double-angle and double-channel braces are among the common steel structural systems resisting lateral loads. In this paper, the parameters influencing the BSCBF seismic behaviours are investigated under cyclic loading. For this purpose, nonlinear finite element analyses of a single-bay single-story frame are employed, and the results show that increasing the number of stitches or decreasing their distances along the length of the built-up members may not necessarily improve the behaviour of the braced systems. That is, inelastic deformation concentration probably occurs in individual elements between stitches, resulting in earlier failure of braces. Moreover, the failure results of the built-up brace members display that the usage of vertical stitch connectors (parallel to the webs) should be avoided in all BSCBF systems in comparison with lateral-stitch braces (parallel to the flanges). In addition, the failure results of double-channel back-to-back BSCBFs are much better than those of similar face-to-face ones. The results of the double-angle diagonal braces also reveal that the failures of the back-to-back brace sections occur earlier in comparison with similar face-to-face or toe-to-toe braces.