Axial Compression Behavior of Fire-Damaged Concrete Cylinders Confined with CFRP Sheets

摘要

This paper presents the axial compression behavior of standard empty set150 x 300 mm concrete cylinders after exposure to elevated temperatures of 300, 500, and 700 degrees C for heating periods of 2 h (for all temperatures) and 3 h (only for 700 degrees C). A total of 192 specimens were tested in static compression to investigate the stress-strain relationships and failure modes of fire-damaged concrete before and after strengthening with carbon fiber-reinforced polymer (CFRP) wraps. The test results showed that the exposure temperature and duration, unconfined concrete strength, and cooling method (air or water cooling) influence the postfire compressive strength, strain at compressive strength, and modulus of elasticity of concrete. Low-strength concrete is more susceptible to the loss in residual properties caused by fire than high-strength concrete. The CFRP wrapping can significantly enhance both strength and ductility of concrete after exposure to elevated temperatures. The level of strength enhancement by CFRP confinement for fire-damaged concrete is higher than undamaged concrete. The confinement effectiveness increases with an exposure temperature, especially for the lowest-strength (20-MPa) water-cooled concrete. In contrast, the level of ductility enhancement on fire-damaged concrete is lower than undamaged concrete. The application of an equation to predict the compressive strength of CFRP-confined fire-damaged concrete is also discussed. It was found that the equation conservatively predicts the ultimate strength of CFRP-confined fire-damaged concrete. However, the prediction becomes less accurate as exposure temperature increases. (C) 2016 American Society of Civil Engineers.