A Study on Ultimate Strength of Folded Steel Plate Girders.

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In this research, the stability strength of steel plate girders assembled by folded web plates and flange plates under equal end moments about their strong axis are investigated. This paper compares experimental buckling resistances of I-shaped steel girders having unfolded web plates with those of the folded plates. The tests show that the buckling resistances of the girders with folded webs can be higher than those of conventional I-shaped girders.To analyze the ultimate carrying capacity of folded steel plate girders with initial imperfections due to initial deflections and residual stresses caused by welding, an elasto-plastic finite element analysis was used based on geometric and material non-linear isoparametric shell elements. It was assumed that material constitutive relationship follows the Von Mises yield criterion and the Plandtl-Reuss plastic flow rule, combined with material and geometric invariance law, strain hardening law and linear unloading law. The non-linear behavi … More or is solved numerically according to both the Newton-Raphson and the Updated Lagrangian formulations where the displacements increase step-by-step. Actual measurements were used for the initial imperfections of residual stress and initial deflection. The ratio of the test results to analysis results for the ultimate carrying capacity is between 0.98 and 1.028, with an average of 0.996. Thus, it may be concluded that this analysis is quite accurate in evaluating the ultimate load carrying capacity of folded steel plate girders.A parametric study using nonlinear finite element approach is also conducted to evaluate the effects of folded angle, width thickness ratio of plate, slenderness ratio of beam, residual stress and yield stress ratio on the ultimate strength of folded steel plate girders. This paper also presents the instability classification of folded steel plate girders based on the parametric study. Three buckling modes are confirmed, i.e., an inelastic lateral-torsional buckling mode, an inelastic local buckling mode and an interactive buckling of the two. From a parametric study, it appears that the effects of folded web element on the ultimate strength of folded steel plate girders. Less