Diaphragm Effects on Ultimate Strength of Horizontally Curved Thin-Walled Box Girders.

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1.An analytical procedure is proposed to predict ultimate strength and nonlinear behavior of thin-walled, welded steel box-girder curved in plan and stiffened by intermediate interia diaphragms. In the approach, the effects of finite deformation, yielding of material under combined bending and St. Venant's torsioning, unloading caused by strain reversal, spreads of yielding, unloading and reloading zones in the cross-sections and along the gider, and residual stress due to welding are all taken into account in flexure analysis by nonlinear finite element method. How to consider local buckling of component plates and distortional warping in the nonlinear flexure analysis is also proposed.2.The comparison of the analytical with the experimental results on the ultimate strength was judged satisfactory.3.The local buckling of component plates can be evaluated by the proposed model of stress-strain curve allowing for plate buckling as shown in Fig. 3 and this model can be incorporated into … More the nonlinear flexure analysis.4.The breadth of buckling plate can be taken to be width of the compressive flanges of the cross-section of the girder and equal to the depth of the compressive zone of the web plate.5.The constitutive model predicted the local buckling compared well with the experimental results.6.The effect of distortional warping can be simulated in an incremental way at the initial strain-state in the nonlinear flexure analysis, where the strain increments for distortional warping are applied in a step-by-step procedure until an external distortional moment is reached.7.From lower level of loading, bowing deformation which is characterized by covnex form was experimentally confirmed at the compressive part web plate. This phenomenon might be considered to be that the cross-sectional part in compression in the curved girder acts as so-called nonlinear behavior of column with initial crookedness.The above results on the model tests in the conclusions are based on a limited amount of experimental work. Research is clearly needed on the experimental program of larger amount of the model-tests. Though some verification is necessary if the proposed constitutive models allowing for local plate-buckling is to be applied to the girder also stiffened by horizontal and/or vertical stiffeners, the assumed breadth of buckling plate is generally conservative. Less