| Concrete cracking is an urgent problem in the field of civil engineering.Steel fiber reinforced concrete(SFRC)is a new type of composite material with excellent properties,which is based on concrete and reinforced by randomly distributed steel fibers.It can hinder the development of microcracks and macro-cracks in concrete.Therefore,steel fiber reinforced concrete(SFRC)is gradually applied to airport pavement and bridge deck structures which require high cracking of concrete.At the same time,many structures with high requirements for concrete cracking need to bear cyclic loads.The structure under fatigue load is prone to brittle failure under static load,which seriously endangers the safety of the users and users of the structure.Therefore,the fatigue performance of steel fiber reinforced concrete and plain concrete is studied in this paper.According to the round panel test method of ASTM C1550,75 specimens were tested under equal amplitude cyclic loading.The fatigue tests of steel fiber reinforced concrete(SFRC)with different steel fiber content(20%,30%,35%),different types of steel fiber(3D,4D,5D),different stress levels(0.6,0.75,0.9)and different aspect ratios(65,55)were compared with those of plain concrete.The deformation characteristics and the influence of fatigue life of SFRC round panels were studied by comparing SFRC content,SFRC type,stress level and aspect ratio.At the same time,ANSYS workbench is used to carry out finite element numerical analysis to simulate the distribution of displacement,stress and fatigue life of round panel specimens,and further predicting the fatigue life of round panels under different stress levels.The main research results are as follows:(1)The failure modes of plain reinforced concrete round panels are mostly three main cracks extending from the center of the bottom of the round panel to the surrounding area between the two supports.At the same time,there are three crushing tracks on the panel surface,which are similar to the characteristics of bending failure of concrete members.After unloading,the three parts are still connected as a whole due to the pulling effect of steel fibers at the cross section.(2)Characteristic of load-deflection curve after fatigue loading;mid-span deflection of circular plate increases with the number of cycles:mid-span deflection increases rapidly when the number of cycles is 10000;after 10000 cycles,mid-span deflection increases sharply;before the first crack appears,the curve approximates a straight line,the slope is large,and the deflection increases slowly.(3)The characteristics of load-mid-span deflection curves under initial static load and after fatigue load are analyzed,and the effects of steel fiber type,steel fiber mass content and stress level on load-mid-span deflection curves under fatigue load are obtained.(4)Ordinary concrete round panel and 5D steel fiber reinforced concrete round panel are more in line with two-parameter Weibull distribution;3D steel fiber reinforced concrete round panel is more in line with logarithmic normal distribution when steel fiber content is 20 kg/m~3,more in line with two-parameter Weibull distribution when steel fiber content is 35 kg/m~3;4D steel fiber with length-diameter ratio 55 is more in line with logarithmic normal distribution when steel fiber content is30 kg/m~3,and steel fiber content is more in line with logarithmic normal distribution.When the ratio of length to diameter is 65,the distribution of 4D steel fibers is more lognormal.(5)The S-N curves of average fatigue life and P-S-N curves considering failure probability of plain concrete and 3D steel fiber reinforced concrete round panels are fitted.(6)The mid-span deflection and fatigue life of the round panel simulated by finite element method are in good agreement with the test results,and the failure mode of the round panel is in agreement with the test results.(7)GM(1,1)grey prediction model for fatigue life of plain concrete and 3D steel fiber reinforced concrete is established on the basis of experimental and finite element simulation results. |
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