| Summary: | 碩士 === 大漢技術學院 === 土木工程與環境資源管理研究所 === 106 === This study uses SAP2000 for non-linear buckling analysis, validates the predecessors' theoretical equation for the effective length and critical buckling force of a top chord in half-through truss bridges, and proposes non-linear buckling to calculate an effective length coefficient, so as to determine the design pressure strength.
The bracing in the horizontal direction of a half-through truss bridge influences the overall buckling mode of the half-through truss bridge and impacts the critical buckling force of the top chord significantly. The rigidity of connection between the floor beams and the vertical member as well as with diagonal members , which cannot be neglected in a bridge design.
The top chord of a half-through truss bridge in the case herein is regarded as a compression member with elastic support and disregards the flexural stiffness of the diagonal web member. The method proposed by scholars Engesser, Bleich, Timoshenko, Lutz & Fisher and Holt is conservative for calculating the effective length coefficient. Considering the flexural stiffness of the diagonal member, the method of Timoshenko, Lutz & Fisher is still conservative for calculating the effective length coefficient of the top chord of half-through truss bridges, and only the method of Engesser, Bleich, and Holt is not conservative.
Nonlinear buckling analysis shows that if the top chord of half-through truss bridges has initial imperfections, then the effect on the critical buckling force of the bridge is slight, because the initial curved form is not completely coincident with the buckling mode. In addition, reinforced concrete decking can slightly increase the critical buckling force of the top chord.
The design compression strength of a steel column is influenced by the residual stress, initial imperfections, and elastic or inelastic buckling of a steel member and the yield strength of steel. The effective length corresponding to the critical buckling force obtained by non-linear buckling analysis shall be calculated by using the Euler equation, and then the allowable pressure or design compression strength of the top chord in half-through truss bridges is determined according to bridge specifications.
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