HYSTERETIC CHARACTERISTICS OF STEEL BARACED FRAMES : Part 1, The Behaviors of Bracing Members under Cyclic Axial Forces

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Abstract
Some recent experimental and theoretical researches have demonstrated that the restoring force characteristics of steel braced frames under cyclic horizontal loads were represented by Reversed-S type loops, and the behaviors of bracings have much influences on the shapes of these hysteresis loops. But the available informations regarding to post-buckling behaviors of bracings under cyclic axial forces are few and much remains to be done. In this paper, we extended the concept of plastic hinges to include plastical deformations, both rotation and contraction, under combination of bending moment and axial force, following to the plastic flow theory. This method was applied to the analysis of the behaviors of bracings under cyclic axial forces. The results of this research are as follows (See Fig. 3-15) 1) The shapes of hysteresis loops are much influenced by the slenderness ratio of the members. 2) Both the maximum strength and the initial stiffness at each half cycle decrease according to increase of loading cycle numbers. 3) a. In short-column range, the maximum strength and the initial stiffness reduce gradually and linearly. b. In intermediate-column range, the compressive maximum strength reduces abruptly, while in another range gradually. c. In long-columu range, the initial stiffness reduce abruptly.

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