OVERLOADING OF PRESTRESSED-CONCRETE SPREAD BOX-BEAM BRIDGES

An analytical scheme is developed that simulates the elastic and inelastic flexural response and the mechanism of damage initiation and propagation for prestressed-concrete spread box-beam bridges under any loading. The scheme employs the finite-element displacement method in which the nonlinear structural response is simulated by piecewise linearization of the tangent stiffness formulation. Damage initiation and propagation are simulated by dividing plate and beam elements into multiple layers, each in plane stress. The influence of box-beam torsional stiffness on the transverse flexure of the superstructure is incorporated into the model by introducing road finite elements possessing the St. Venant torsional rigidity of the actual box section into the plane of the bridge slab. The coupled flexural and axial components of the box-beam contribution to composite bridge action are retained in twin I-beams, each corresponding to half the box beam. The model is applied to a field-tested bridge and found to yield reasonably good, slightly conservative predictions of elastic bridge deflections and girder moments. Results of postelastic simulations of several box-beam bridges are compared with those of flexurally identical or comparable I-beam bridges. Spread box-beam bridges are found to possess superstructure stiffness and strength approximately 30 percent higher than their I-beam counterparts. The lateral distribution of moment among box girders, more favorable at elastic load levels, is maintained almost proportionately well into the inelastic range, whereas progressive and unstable concentration of moment toward the loaded girder or girders is observed in comparable I-beam superstructures.