Experimental Research On Flexural Fatigue Properties Of Steel Fiber-reinforced Concrete Beams At Low Temperatures

In virtue of the excellent tensile strength, flexural strength, impact strength and fatigue strength, preferable ductility and crack control ability, the steel fiber reinforced concrete (SFRC) has been diffusely applied to civil engineering. On the base of the domestic and overseas fatigue research, tests were designed and flexural fatigue life, distortion and damage evolvement properties were researched according to the basic mechanics property investigation of SFRC at low temperatures. It was discovered that the uniaxial compressive strength of SFRC at low temperatures was less than that under standard condition;the flexural strength of SFRC was more than that under standard condition;b oth the uniaxial compressive and flexural strength increased as the temperature fell. The fatigue distortion process of SFRC at low temperature can be divided into latency stage, stable development stage and instability development stage. The flexural fatigue life of SFRC beams at low temperatures obey double logarithm fatigue equation, which were lg S = 0.07659-0.0563 lg N (-7℃) , lgS = 0.1:5517 - 0.09083 lg N (-12℃). The double logarithm fatigue equation gained through the test can be utilized as approximate fatigue life estimation. It was discovered that the flexural fatigue life submit Weibull distributing after validation as the the discrete data and the P-S-N equation was founded. The flexural fatigue remnant strain process can be divided into latency stage, stable development stage and instability development stage. The equations of flexural fatigue second stage strain velocity and stress level of SFRC beams at low temperatures were gained: lg (ε|·)_sec =3.445×10^-7 + 6.102×10^-5 lg S(-7℃), lg (ε|·)_sec= 2.181 × 10^-7 + 3.211×10^-5 lg S(-12℃). The fatigue elastic modulus attenuation velocity under high stress level was more than that under low stress level. The damage evolvement process can be divided into latency stage, stable development stage and instability development stage. The damage evolvement velocity under high stress level was more than that under low stress level.