Study On The Bending Fatigue And Damage Properties And Micro-strength Of Steel Fiber Reinforced Concrete

Theoretic and experimental research on the bending fatigue and its damage properties of Steel Fiber Reinforced Concrete (SFRC) under several stress levels constant amplitude loading is carried out in this paper, and the experimental data of fatigue life, strain and degradation of bending modulus are obtained. Based on the experimental results, fatigue life distribution of SFRC is studied using fatigue life statistics theory, the fatigue life equation is established, and some experimental formulas for evaluating strain and degradation of bending modulus are gained. The fracture procedure of material under fatigue loading is a micro-damage cumulative procedure. According to the fatigue cumulative damage theory, a cumulative damage model for bending fatigue of SFRC is derived. SFRC can be simply looked as a kind of composite material composed of steel fiber and concrete, so tensile stress distribution in steel fiber and shear stress distribution in interface when tensile loading is applied on SFRC are derived by using shear-lagging method. The probability density functions of fibers?distribution in concrete are established according to the geometric models of fibers?distribution in concrete. Based on these results, the tensile strengths of aligned fiber reinforced concrete and random fiber reinforced concrete are derived, furthermore, the first-crack strength and the limited strength of random fiber reinforced concrete are also obtained from interfacial debonding theory. The study results in the paper can be concluded that the bending strength of SFRC is much higher than that of plain concrete and bending fatigue properties of SFRC are better than that of plain concrete, that bending fatigue life of SFRC can be described by two parameter Weibull distribution, and that the fatigue life eql~ation, experimental formulas and the cumulative damage model can describe correctly the bending fatigue behaviors of SFRC. Theoretic study results indicate that using composite material micro-mechanics can establish the relationship between micro-structure parameters and macro-mechanic properties of SFRC, which is significant to understand the reinforce mechanism and to conduct micro-design of SFRC.