Design for crack control in concrete structures on ground exposed to imposed strains

Design recommendations are proposed for the prevention of cracking in concrete structures on ground exposed to imposed strains from temperature or shrinkage. Restraint stresses were calculated with a two-dimensional finite-element model, where concrete is simulated with plane four-node elements and the frictional surface with non-linear contact elements, taking into account both horizontal and vertical movements. The calculations were performed incrementally with stepwise changes in temperature loading. Imposed strains with a gradient over the thickness give restraint stresses significantly higher than uniformly imposed strains. It is shown that superposition can be used to estimate the total stress from a combination of simplified elementary strain profiles. Recommendations for design are given based on comparisons of the finite-element results and results from simplified theoretical methods. Recommended design values for imposed deformation are also given. The simplified methods give good estimations for thin and slender structures.