Numerical investigation of imperfection-induced secondary bending stresses in box girders

Numerous studies have demonstrated that the initial out-of-plane deflection can significantly affect stress distribution along the web boundaries of steel plate girders, potentially leading to the initiation of fatigue cracks and eventual structural failure over time. Fatigue cracks in thin-walled structures commonly initiate at locations of maximum secondary bending stress, arising from the web imperfections introduced during the complex manufacturing process and further amplified by the interaction of global and local stresses. The secondary bending stress of box girders web plate has been numerically investigated in this article. Several nonlinear static analyses have been performed, using the hybrid parametric FE model, consisting of shell and beam finite elements. Vertical normal stress in the upper web boundary below rail was evaluated under different boundary conditions and geometric modifications. Considering the deflection shape of critical buckling mode 1, the directional effects of initial web imperfection and eccentric moment have been evaluated. Also, a comparison in terms of secondary bending stress at different girder spans, intermediate plate spacing and load positions are discussed. The results of this study offer valuable insights into the most and least favorable scenarios related to geometric modifications and varying loading conditions, while also highlighting existing research gaps in current design codes.