Thermally induced stresses in composite steel-concrete bridges are higher than those experienced by their concrete and steel cousins due to dissimilarity in material properties. These thermal stresses are relatively high when compared to service load stresses, leading to significant damage that manifest itself in terms of crack development in the concrete deck. This in turns leads to the corrosion of the steel reinforcement, steel superstructure, along with the deterioration of the concrete through water seepage. The various bridge design codes emphasize the importance of thermal stresses by providing designers with suggested thermal gradients that account for the temperature differential in bridges. However, previous studies have failed to account for the pre-existing construction transverse cracks in the concrete deck and their effect on the temperature distribution in composite bridges.In this study, a three-dimensional finite element model was developed to investigate the temperature distribution in a selected case study bridge. The model is a realistic depiction of an existing bridge with pre-existing transverse deck cracks and actual environmental boundary conditions for a selected geographical region. The results of a thermo-elastic analysis show that the AASHTO LRFD Bridge Design Specification is overly conservative and overestimates the vertical temperature gradient for the studied bridge. The AASHTO and other models found in existing literature seem to ignore the nonlinear thermal gradient for composite bridges, which produces a nonlinear strain component that can be critical for the bridge design and cannot be treated in a trivial manner. In addition, the pre-service deck transverse cracks appear to have a considerable effect on both, the vertical and the longitudinal temperature distributions in composite steel-concrete bridges, and hence require further assessment.
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