Study on Stiffness and Ultimate Behavior of Multi-Planar Joints for Tubular Space Trusses

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The ultimate behavior of tubular double K-joints, which are the most representative joints among diverse multi-planar joints, was studied. Two types of ultimate capacity equations for double K-joints under symmetrical axial brace loading were derived from this study. The first one has the best possible accuracy with a coefficient of variation (COV) of 0.06, while the second one was simplified by relinquishing accuracy slightly (COV=0.1). Ultimate capacity equations with good accuracy were also derived for double K-joints under anti-symmetrical axial brace loading. These equations are based not only on experimental results but also on finite element analysis results, the latter ones having been obtained through a cooperative research with investigators in University College Swansea. Another important topic that our strength prediction equations proposed in the past may err on the unsafe side for joints with extremely heavy chords, which was argued by the same investigators in Swansea, w … More as also studied. Both experimental and numerical results showed that our proposed equations are applicable to joints with such heavy chords. Through these investigations some principal requirements for combining experimental and numerical results to evaluate ultimate capacities of tubular joints were found.From this onvestigation the ultimate behavior of multi-planar joints was made clear. Efforts are now being continued to establish design rules applicable to all the multi-planar joints. A few tentative desigh equations have already been proposed. For this purpose a database including 2000 data sets (joints) from both experimmental and numerical results have been prepared.With regards to interactions between frame and joint behavior, the following conclusions have been drawn :1. When a failure of a joints is the first failure event in a truss structure, our proposed ultimate capacity equations accurately predict the capacity of the joiint.2. When bucking of a member is the first failure enent, joints fail at loads lower than those predicted by our wquations owing to stress re-distribution taking place after bucking of members.3. The ultimate behavior of trusses after bucking of members can be reproduced by an analysis that takes into account effects of stress re-distribution. However this analysis is too complex for the use in design practice. An aternative method of design is to design the joints to have capacities 25% greater than buckling loads of members. In this latter case an earthquake resistant design of truss structures that includes post-buckling energy absorbing capacity bees performed. Less