Short and long term deflection analysis of FRP strengthened RC members

Abstract

The use of fibre-reinforced polymer (FRP) materials has grown steadily in civil engineering for the last decades, and retrofitting of reinforced concrete (RC) structures was not an exception. However, despite its commonly agreed benefits, it can be corrupted by not full composite action of concrete and FRP material. While the structure is not cracked, both elements deform together and it can be considered as a full composite action. However, after cracking of the concrete, the stress concentration appears in the cracks and reduces the contact stiffness of the concrete and the FRP. Therefore, to predict the real deflection response, the actual values of the concrete and FRP contact stiffness and the stiffness of the entire element are required. The recently proposed calculation technique based on the built-up bars theory by the authors has proven to be appropriate for prediction of the short-term deflection response. However, the strengthened members operate under sustained load action. Against this background, a new improved analytical solution is proposed that covers the effects of both shortand long-term loading. Such a prediction model based on the general laws of deflection and the built-up bars theory improves the current state-of-the-art by allowing full prediction of the deflection response of the retrofitted member at each stage of the structures live cycle, including the effects of prestressing and partial stiffness of the concrete-FRP joint. An extended database of retrofitted element studies was also compiled for the experimental validation of the proposed methodology. The results validate the proposed methodology, which could be considered for practical application in the design of retrofitting of real structures.