Influence of Nonuniform Box Beam Dimensions and Bridge Transverse Slope on Environmentally Induced Stresses in Adjacent Box Beam Bridges

The service life of adjacent box beam bridges is curtailed by the corrosion of reinforcement in the girders and spalling of concrete. This damage is attributed primarily to infiltration of water and chemical agents through longitudinal cracks in the shear keys. However, there are two other possible factors that can lead to water penetration of the bridge structure and eventual failure in box beam bridges: nonuniform box beam dimensions and bridge transverse slope. No study has been conducted to evaluate the effects of these two factors on induced stresses in adjacent box beam bridges. Typically, box girders are placed together with a transverse slope to facilitate drainage, which creates contact areas along just the bottom edges of adjacent girders. Additionally, for girders with nonuniform dimensions, even if within beam dimension tolerance, the contact between adjacent beams may be created at isolated spots. Measurements made at a box beam fabrication site verified inconsistency of beam dimensions. Three-dimensional finite-element models of composite and noncomposite single-span skew-adjacent box beam bridges were created to determine the stresses induce at the contact areas under environmental load conditions. The finite-element model was calibrated and validated in terms of the stresses in tie bars using experimental temperature profiles (uniform with and without temperature gradient). Two models were analyzed; the first model represented the contact areas generated due to drainage slope and the second one represented nonuniform beam dimensions using realistic input data. Under uniform and temperature gradient conditions, the models showed that contact stresses exceeded the concrete design strength at certain spots along the beams’ length. For girders with full flat contact, the contact stresses were noted to be less than the concrete strength. Additionally, the results of the analysis showed the contact stresses were reduced when modeling a bridge with a reinforced concrete deck. Moreover, the skew geometry showed a significant effect on the distribution of stresses at contact zones. Furthermore, the finite-element failure mode was compared with past research in terms of the locations of the greatest deterioration, and good agreement was found. Based on the results, it is recommended in this study to construct box beam bridges with enough spacing between the beams to ensure that no contact occurs between them; it is also recommended to manufacture box beams with high levels of accuracy.