Predicting Deflections of Reinforced Concrete Beams Analytically

Abstract

A rational method of analysis is proposed for the calculation of creep deflections of reinforced concrete beams under sustained service loads. The method introduces the use of a fictitious modulus relating, for a given section under bending, the initial stress in concrete with the final strain after a period of sustained load. The requirements of strain compatibility and equilibrium of a section are used, in conjunction, to determine the position of neutral axis and strain and stress distributions after creep. The long‐term flexural rigidity of the member, (EI), is determined from a knowledge of a new neutral axis and a new modular ratio and is used to calculate the final deflections. The approach for calculating long‐term deflections is similar to the current American Concrete Institute (ACI) procedure for calculating short‐term deflections. The accuracy of the analysis is verified by comparison with several experimental measurements of beam deflections. The result is good correlation between the theoretical values and measured values.