Fire performance of insulated CFRP-strengthened RC beams with different anchorage systems: Experimental and numerical investigation

This paper presents an experimental and numerical investigation into the fire performance of reinforced concrete (RC) beams strengthened with externally bonded carbon fiber-reinforced polymer (CFRP) sheets and protected by various anchorage and insulation systems. Seven full-scale beams were tested, including three specimens under ambient conditions and four exposed to the ISO 834 standard fire curve. The key parameters examined included insulation schemes, such as a 20 mm cement-based fire-resistant plaster (SJ-2) and a hybrid system combining 2 mm intumescent coating with a 20 mm mortar or SJ-2 layer, as well as the anchorage configurations including mechanical anchors and CFRP U-wraps. Experimental results showed that all insulated specimens achieved a fire-resistance rating of at least 2.5 hours without failure. The combined application of insulation and anchorage systems effectively reduced midspan deflections during fire exposure, primarily by preserving the tensile contribution of the CFRP sheets. A coupled thermal-mechanical numerical model was developed by integrating transient heat transfer analysis with a fiber-based sectional approach. This model explicitly accounted for the temperature-dependent degradation of concrete, steel reinforcement and CFRP sheets. Numerical predictions closely aligned with the experimental results, which accurately predicted the temperature distributions across the beam cross-sections and the degradation of flexural capacity. The validated model serves as a reliable tool for simulating the fire response of CFRP-strengthened RC beams with various anchorage and insulation systems, thereby offering a basis for optimizing fire protection designs and providing a reference for engineering practice in enhancing fire resistance using anchorage systems.