Analytical study of horizontally curved hollow tubular flange girders

A tubular flange girder bridge is an innovative steel curved highway bridge girder system, which uses I-shaped steel girders with rectangular tubes as flanges. Compared to conventional I-shaped plate girders, the increased torsional stiffness provided by the tubular flanges dramatically improves the structural behavior of curved tubular flange girders, resulting in substantially reduced deflections, cross section rotations, and stresses. This research investigates the behavior and design of curved tubular flange girders for highway bridges.;First, finite element (FE) models of straight tubular flange girders with hollow tubes (HTFGs) are developed. A parametric study is performed using the FE models to study the effects of stiffeners, geometric imperfection, residual stresses, cross section dimensions, and bending moment distribution on the lateral-torsional buckling flexural strength of HTFGs. These analytical results are used to evaluate formulas for determining the flexural strength of HTFGs.;Then, FE models for curved hollow tubular flange girders (CHTFGs) are introduced. The models consider material inelasticity, second order effects, initial geometric imperfection, and residual stresses. A parametric study is performed on both individual girders and three-girder systems braced by cross frames to study the effects of web stiffeners, tube diaphragms, geometric imperfection, and residual stresses on the load capacity of CHTFGs. The results indicate that using a suitable arrangement of transverse web stiffeners and tube diaphragms effectively eliminates the influence of cross section distortion on the load capacity. The effects of initial geometric imperfection and residual stresses on the load capacity of CHTFGs are shown to be small.;The FE models are used to study the deflections, cross section rotations, and stresses that develop in individual CHTFGs and three-girder systems of CHTFGs under dead and live loads. The results for the CHTFG systems are compared with results for corresponding conventional curved I-girder systems. The effects of the curvature, cross section dimensions, number of cross frames, and a composite concrete deck are investigated. The results presented in this study suggest that CHTFGs are more structurally efficient than curved I-girders and may not need temporary support or bracing during construction.;Design criteria based on 2004 AASHTO LRFD Bridge Design Specifications (2004) are used to design CHTFGs. Simplified FE models are developed to determine the load demands corresponding to different limit states. Accurate FE models are used to verify the capacities of the CHTFGs. A design study based on nine different CHTFG bridges is performed to evaluate the adequacy of this design approach. It is verified that the design criteria in AASHTO (2004) can be used for the design of CHTFGs.