Quantifying Residual Strength of Cement-Based Reinforced Composites Under Repeated Loads

Recent structural engineering trends revealed that fiber-reinforced polymers (FRP) define an efficient replacement for steel because of their lightweight and corrosion resistance. However, the unfavorable environment (elevated temperature and humidity) can affect the long-term resistance of those materials. Therefore, this study analyzes the adverse effects of environmental conditions and repeated mechanical loads on the composite performance of concrete beams reinforced with FRP materials. A new testing layout and a simplified analytical model are developed to quantify the flexural stiffness decay. This model relates the particular moment and curvature values, requiring neither iterative calculations nor the load history. Thus, this exceptional feature ensures the explicit quantification of the equivalent strength and comparative analysis of the residual efficiency of the composite systems with different reinforcement layouts and materials. This study compares several reinforcement schemes and considers the open atmosphere corresponding to the Nord Europe climatic region and the reference laboratory conditions. The analysis reveals that the outdoor environment specifically affected the stiffness of the external bonded reinforcement system under repeated loading. In contrast, the near-surface mounted reinforcement was resistant to this effect.