MECHANICAL BEHAVIOR OF NORMAL CONCRETE UNDER TRIAXIAL COMPRESSION AFTER HIGH TEMPERATURE

Triaxial equal proportionable compressive tests on C30 normal concrete samples subjected to 200 ℃―600℃ were performed, using a large-scale dynamic-static triaxial concrete test system at the State Key Laboratory of Coastal and Offshore Engineering. The failure modes of samples are observed, and the triaxial strength, strains at peak stress, and stress-strain curves are recorded. Test results show that, triaxial compressive strength is greatly larger than uniaxial strength for the same designated temperature, and middle stress has significant influence on both tri-axial compressive strengths and strains at peak stress. In addition, with the increase of suffered temperature, the drop rates of tri-axial compressive strength are different from those of uniaxial compressive strength. Relative to uniaxial compressive strength, the increase in both normal stress strength and shear stress strength in octahedral stress space becomes more significant with the further increment of suffered temperature after 200℃. The influence of stress ratio and temperature on triaxial compressive strength is analyzed, and a regression equation describing relationship among triaxial compressive strength, stress ratio, and temperature is proposed in octahedral stress space，which can provide experimental and theoretical foundation for mechanical analysis of concrete structure suffered from high temperature under complex stress condition.