Effective Moment Of Inertia And Deflections Of Reinforced Concrete Beams Under Long-Term Loading

Abstract

The paper presents a method for estimating long-term deflections of reinforced concrete beams by considering creep and shrinkage effects separately. Based on equilibrium and compatibility conditions a method is developed for investigating the properties of a cracked transformed section under sustained load. The concept of effective moment of inertia is extended to predict initial-plus-creep deflections. Long-term deflections computed by the proposed method are compared with the experimental results available in the literature and with the values obtained by the ACI Code method. This comparison shows that for beams having span/thickness ratio greater than 25, the ACI Code method underestimates long-term deflections while the proposed method gives a better estimate with computed to measured deflections ratio equal to 1.0.