Estimation of shrinkage effects on reinforced concrete podiums

Abstract

The shrinkage of concrete often creates cracking problems in large podium structures. The long-term effects of shrinkage and creep in a concrete structure may be estimated by analysing it as a plane stress problem with the supporting walls and columns modelled as springs having suitable stiffnesses. The variation of stresses and strains may be obtained by time integration based on the conventional creep coefficient, time-dependent concrete modulus and shrinkage strain. Using a simplified one-dimensional model, the effects of structure size, support stiffness and stage construction on the induced stresses are investigated. Results show that the magnitude of induced stress normally increases with the member length and support stiffness. The rate of stress increase also depends on the support stiffness. An extensive parametric study is carried out to investigate the use of stage construction in controlling shrinkage stresses particularly focusing on the effect of time-lag and size of late-cast strip. Design charts are prepared for estimation of shrinkage stresses for simple cases. Examples of rough estimation of shrinkage stresses in two-dimensional cases are presented. Recommendations are also given for provision of reinforcement for crack control.