Existing design specifications used in North America and Europe do not directly treat the general limit state of local collapse of tubular truss chords at bearing supports; although these specifications do consider the very specific case related to chord wall resistance under concentrated loads applied through simple gusset plate or tubular branch connections. The lack of general and robust treatment of chord bearing strength represents an unsatisfactory situation given the fact that very large reaction forces are often applied locally to the ends of chord members with slender cross-sections in long-span overhead highway sign trusses. A number of these structures in the U.S. have been shown to be inadequate for this limit state; a situation precipitating costly retrofits, construction delays, and motorist safety concerns. This dissertation research is aimed at quantifying the bearing strength of circular chords in long, simple-span tubular trusses. Two (2) full-scale experimental tests were conducted at the University of Pittsburgh as part of the current research effort. In addition, a parametric study based on the finite element (FE) method is also carried out. The nonlinear FE modeling techniques are first validated against the experimental testing results and then employed in a parametric study whose results are reported on herein. The current study reveals that the bearing strength is influenced by the geometry of the bearing region including any adjacent intermediate truss member(s), the nature of loading, and the material properties. Using a semi-empirical approach, general capacity equations for predicting the ultimate bearing strength is developed. Capacity equations are developed for axial loading (P), moment (M), and interaction of both (P+M).
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