Shrinkage effects on cracking and deflection of concrete structures

In the assessment of the ultimate limit state, concrete contribution in tension is rarely  considered. However, as the additional stiffness provided by concrete in tension is significant at service, accounting for concrete contribution in tension is critically important  for serviceability limit state prediction of reinforced concrete elements. Both numerical and analytical methods for predicting deflection and cracking have used concrete contribution in tension in predicting serviceability performance. Given the significance of the concrete contribution in tension, for the serviceability limit state, accurate modelling of the tension capacity of concrete has become extremely important. Concrete contribution in tension is often influenced by the shrinkage and expansion condition of the concrete. Lack of shrinkage strain that can be imparted on the test specimen under experimental conditions, often limit our understanding to quantify the real influence of shrinkage conditions on the serviceability  performance of concrete structures.  There are however enough records that the reinforced  concrete under different shrinkage conditions have very different serviceability performance. In particular, some records have shown shrinkage conditions have more than doubled the deformation and cracking of concrete at service. This study has developed to understand the real implication of shrinkage and expansion of serviceability limit state performance. The study uses tension elements subjected to both shrinkage and expansion conditions for the experimental investigation. A total of 28 tension specimens and 6 flexural elements under different shrinkage and expansion regimes ranging from -450 με to +2000 με form the basis of the experimental investigation. Test results indicate the influence of shrinkage conditions on the tension-stiffening effect of concrete and the serviceability performance of reinforced concrete elements. Results also confirm the limitation of the use of shrinkage and expansion conditions measured in the companion samples to predict the service performance of reinforced concrete and the importance of considering the effect of  associated creep in the prediction. Based on the extensive experimental results this research  study proposed and validate a method to account for associated creep under shrinkage and expansion of concrete. The proposed method based on the shrinkage measured from  companion samples and adjusted for possible relaxation has provided good serviceability limit state performance of tension elements and bending elements subjected to wide-ranging  expansion and shrinkage conditions. It is shown that the loss percentage of the restrained force is as high as 60% of the applied shrinkage and expansion conditions and is attributed largely to the lack of development of the microstructure of the concrete at the early age where shrinkage and expansion forces are considerable. This study shows the importance of the adjustment of free shrinkage expansion and confirms the relevance of accounting for the part of shrinkage and expansion lost due to possible creep relaxation for accurate prediction of member response. Starting from correction to tension stiffening behaviour of concrete subjected to shrinkage and expansion conditions study extended its work to serviceability limit state predictions of deflection and cracking of reinforced concrete elements subjected to shrinkage and expansion conditions and prove that the adjustment proposed consistently  provides accurate predictions both for flexural elements and tension elements.