Investigation into Hysteretic Behavior of Tubular Trusses with Flexible Joints

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Trusses of thin-walled tubular members are known to be strong, stiff and light, but show limited energy absorbing capacity under dynamic loads with the exception of highly redundant trusses. The ultimate capacity and ductility of circular tubular trusses under large alternating deflection are the subject of this study.Tests have been conducted on complete trusses of tubular members with welded K-joints under cyclic loading. Observed modes of failure include buckling of braces and failure of joints, which occurred in interaction as the cycling progressed. Interests are focused on the effective length for braces, the post-buckling behavior of braces and trusses, and the participation of joints in failure of trusses.The following conclusions may be drawn from this study.1. All the trusses studied here showed stable ductility without sharp decay in resistance after buckling of the braces, because the chords possessed a considerable reserve of capacity. Making the chords relatively strong in a truss is advantageous to avoid occurrences of brittle failure due to damages concentrated on the most critical panels of the truss during earthquake motions.2. The buckling and post-buckling behavior of the braces was able to be clarified fairy well and was incorporated in the nonlinear frame analysis. The point-hinge analysis was found to be a powerful tool to interpret hysteretic behavior of the truss and be readily applicable to a dynamic analysis. It is worthwhile to note that the point-hinge analysis was conducted on a micro computer in this study.3. Since the resistance of joints deteriorates due to buckling of braces, the joints should be designed to have a greater capacity than the buckling capacity of the braces. However, it is tolerable that the joints sustain modest damages under severe earthquake excitations because joints show significant ductility.