The Experimental Study On Fatigue Crack Propagation Of Steel Fiber Reinforced Concrete Beams

With the increase in traffic volume,the reciprocating load of the concrete structure becomes more and more complex,and the fatigue problem becomes more and more serious.Steel fiber reinforced concrete(SFRC)has the properties of high ductility,crack resistance and fatigue performance.It is widely used in roads,bridges and rail constructions.However,the SFRC has been studied for a short time and its fatigue life,mechanical properties,and fatigue cracks are still limited.Therefore,it is of great significance to explore the fatigue and mechanical properties of the SFRC structures to expand their range of applications.To investigate the fatigue behavior and crack growth of the SFRC beams,9 SFRC beams with different steel fiber incorporation rates were tested under static load and fatigue.Moreover,the effects of the steel fiber incorporation rate on the fatigue life and the failure mode of the SFRC beams were studied.Considering the development of the SFRC beam fatigue crack,firstly,the SFRC fatigue crack growth rate equation and fatigue life evaluation equation was established,and then,the inhibitory effect of steel fiber on the crack width was discussed,finally,the calculation formula was deduced for the SFRC beam crack width.The main research contents of this paper are as follows:(1)The steel fiber mixed with a rate of 0.5%,1.0% and 1.5% of the SFRC beams fatigue test.The curve of the SFRC beam load and deflection and the curve of the steel bar and concrete strain were obtained,respectively.The development pattern of stress and strain of the SFRC beams under cyclic load was summarized,and the effects of steel fiber volume ratio for the SFRC beam deflection,fatigue life,and failure form were studied.(2)The a-N relation of the SFRC beam fatigue crack and the distribution of fatigue crack under different load cycles was obtained.The development pattern of the SFRC fatigue crack was studied,and an SFRC fatigue cracks growth rate model combined with fracture mechanics was established.Otherwise,the Paris formula of fatigue crack growth rate and fatigue life evaluation equation for different steel fiber volume rate was fitted.(3)The variation of the SFRC beam crack width under fatigue load was determined.Based on the theory of calculating the crack width of reinforced concrete,the influence of steel fiber on the crack width was studied,and the formula for calculating the crack width of the SFRC beams under static load and fatigue load was established.According to the test results,the influence parameters of fatigue crack width were fitted.