CREEP AND SHRINKAGE REVISITED

Modern construction techniques enable reinforced concrete structures t o be constructed rapidly. The loads occurring due to the construction process can be as large as the design service load. These construction loads can cause significant immediate deflections due to concrete cra cking and its low early-age modulus of elasticity. Because of the high applied stress-developed strength ratio and shrinkage, the time-depen dent deflections may be unacceptably large. These changes in the const ruction process, together with the increasing use of finite element pr ograms, warrant a review of the validity of current creep and shrinkag e provisions. Based upon a survey of published experimental data, equa tions were developed to calculate the modulus of elasticity, shrinkage , and creep coefficient in terms of developed concrete strength. The t ime function used was the product of a Ross-type relationship for size effects and logarithmic time. The proposed equations, together with t hose recommended by ACI 209-82 and the CEB 1990 Model Code, are compar ed to the published data.