Thermomechanical Loading of FRP-Laminated RC Beams: Numerical Study with Response Surface Methodology Prediction

Abstract This study investigates the thermomechanical behavior and rehabilitation of RC beams strengthened with fiber-reinforced polymers (FRP) under high-temperature conditions, which are critical during fire exposure. A detailed finite-element model (FEM) was developed to simulate the structural performance of RC beams strengthened with three types of FRP laminates: carbon (CFRP), glass (GFRP), and aramid (AFRP). The model captures material nonlinearity, bond behavior, and temperature-dependent properties to analyze the effects of elevated temperatures (up to 800°C) on beam deflection, stress distribution, bending moment, and shear force. The study focuses on identifying the critical temperature at which each FRP type begins to lose effectiveness, providing insights into their thermal resistance. Additionally, the response surface methodology (RSM) was employed to predict and optimize the structural performance under various thermal and loading conditions. The RSM model demonstrated high predictive accuracy ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="upper R squared greater than 0.99" display="inline" overflow="scroll"> <mml:msup> <mml:mi>R</mml:mi> <mml:mn>2</mml:mn> </mml:msup> <mml:mo>&gt;</mml:mo> <mml:mn>0.99</mml:mn> </mml:math> ), validating the reliability of the numerical approach. Results showed that CFRP exhibits superior structural performance and thermal stability compared with GFRP and AFRP, particularly at temperatures up to 500°C. The findings emphasize the effectiveness of CFRP as a reliable rehabilitation solution for fire-damaged RC structures.