Flexural Resistance of Longitudinally Stiffened Curved I-Girders

The current AASHTO Specifications neglect the contribution of the longitudinal stiffeners to the flexural resistance of slender-web I-girders after the webs have undergone bend-buckling. The authors have previously developed a cross-section model to address this conservatism, and proposed a simplified equation to calculate the web bend-buckling factor Rb for straight longitudinally-stiffened I-girders. The recommendations are shown to work well not only for the yield limit state, but also for members with lateral torsional buckling and flange local buckling as the controlling limit states. The model also works well for cases with high moment and high shear. Horizontally-curved girders experience larger flange lateral bending stresses due to curvature, and the Specifications treat the compression flanges of such members as equivalent beam-columns. The current paper examines whether the proposed modified equations for Rb developed based on straight longitudinally stiffened girders can be applied to horizontally curved longitudinally stiffened I-girders within the framework of the current beam-column type equations (termed as the 1/3rd rule). The paper first illustrates that the design of curved longitudinally stiffened girders is always limited to either the yield limit state or the shorter lengths in the inelastic LTB region. The paper also recommends an increase in the curvature parameter, Z from the current value of 10 to 13 using finite element simulations on homogeneous I-girders subjected to uniform moment.

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