A rational method to predict long-term deflections of FRP reinforced concrete members

Due to the low modulus of elasticity of FRP bars, deflection control is often a limiting factor in the design of FRP reinforced concrete (FRP RC) structures. To address long-term deflections due to creep and shrinkage, available codes and guidelines for FRP RC structures, such as ACI 440.1R-06 and CSA-S806-02, propose simplified procedures based on empirical multiplicative coefficients. Although easy to use, these procedures do not account for the influence of changes in material properties or factors affecting creep and shrinkage of concrete. A straightforward method to predict long-term deflections due to creep and shrinkage based on rational multiplicative coefficients deduced from the principles of the Effective Modulus Method (Eurocode 2) is presented. The proposed method, although simple, accounts for main mechanical properties of materials, variations in environmental conditions or other parameters that can affect creep and shrinkage. The method is compared to CEB-FIP, ACI 440.1R-06 and CSA-S806-02 proposals. A good agreement between the CEB-FIP and the proposed method is obtained. However, the coefficients proposed by ACI and CSA can lead to considerable differences in long-term predictions with respect to the proposed method depending on the characteristics of the structure.

► We propose a rational method to predict long-term deflections of FRP RC structures. ► The method is deduced from equations based on principles of structural mechanics. ► The method is compared to CEB-FIP, ACI and CSA procedures. ► The long-term deflections depend on nρ and on the creep and shrinkage of concrete.