Simplified method for the calculation of long-term deflections in FRP-strengthened reinforced concrete beams

Abstract

In this paper, a theoretical study of the time-dependent behaviour of FRP (fibre reinforced polymer)-strengthened reinforced concrete (RC) cracked sections subjected to sustained loading is performed. Based on it, a simplified method for the calculation of long-term deflections has been proposed and verified with available experimental results. The method, which explicitly accounts for the most important parameters involved in the time-dependent behaviour of concrete structures, has been used to study the influence of the FRP ratio on the short and long-term deflections on RC beams. It is concluded that the observed reduction of long-term deflections is mainly due to the reduction of short-term deflections due to the increment of stiffness caused by FRP laminates, and that the constraint produced by the FRP laminates to the long-term increment of curvature is small. Furthermore, the effectiveness of the FRP in reducing long-term deflections depends on the tensile and compressive reinforcement ratios and on whether the FRP laminates are bonded before or after the instantaneous deflection has taken place. Due to its simplicity and accuracy, the proposed method becomes a useful tool to be used at the design stage for the selection of adequate FRP strengthening solutions.