Thermal Stresses in Steel–Concrete Composite Bridges

The objective was to determine experimentally and analytically two-dimensional steady-state temperature distributions produced in the cross-sectional planes of steel–concrete composite simple span bridges. The upper and lower surfaces were exposed to different temperatures.The research included the development of finite element solutions for steady-state temperature distributions from known boundary conditions and the calculation of strains and stresses. Temperature and stress distributions were generally nonlinear with linear strains through the finite elements. Temperatures were predicted to ±1 °F (±5/9 °C). The experimental strains are linear through the composite section, with the computed finite element strains giving generally slightly higher stresses. The conventional and finite element method computed stresses were compared.For positive curvature, the conventional method underestimated the compressive stress in the top flange by about 20% while the bottom flange tensile stresses were identical. For negative curvature, the conventional method overestimated the bottom flange compressive stresses between 15 to 27% and the top flange tensile stresses from 10 to 61%. The concrete slab stresses were overestimated for positive curvature and slightly underestimated for negative curvature. Slab stresses were relatively small when compared with the permissible concrete stress. Temperature stresses in the steel beam were shown to be significantly large, about 30% of the permissible steel stress, to warrant consideration in the design of these bridges. The stresses were calculated for short term steady-state temperatures. Transient conditions existing in the field produce greater thermal stresses.