MECHANICAL PROPERTIES AND CONSTITUTIVE MODEL OF ULTRA-HIGH PERFORMANCE CONCRETE MATERIAL UNDER UNIAXIAL TENSION AND COMPRESSION CYCLES

Ultra-high performance concrete (UHPC) is a new material with high tensile, compressive strength and strain hardening after cracking, which has a wide application prospect in the field of assembled structures. To clarify the mechanical properties of UHPC under uniaxial cyclic loads, prism and dog-bone specimens with different steel fiber content are designed. Through uniaxial compressive and tensile tests with different loading regimes, the effects of steel fiber content, of maintenance mode and, of loading regime on uniaxial mechanical properties of UHPC are analyzed. The test results show that: the peak compressive strain of UHPC with the steel fiber content of 2% is significantly larger than that of UHPC with the steel fiber content of 1% and 3%. The elastic modulus of each UHPC specimen is significantly higher than that of traditional concrete. Furthermore, UHPC shows strain hardening phenomenon and ductility in tensile experiment. The content of steel fiber and steam curing treatment can significantly improve the tensile strength of UHPC specimens. Finally, upon the test data, the skeleton curves and hysteresis criteria of UHPC under compression and tension are proposed, and the formulae for the process of unloading (reloading) are fitted, which can be used for the basic constitutive model of UHPC in the numerical calculation.