Experimental Study On Tensile Fatigue Strength Of Steel Fiber Reinforced Concrete

Due to the anti-crack function of steel fiber in the early stage of concrete cracking,if steel fibers were mixed into plane concrete,not only concrete's tensile and flexure strength,but also its ductility will be improved.After several decades of study at home and abroad,some elementary knowledge of steel fiber reinforced concrete(SFRC)'s static and fatigue mechanical properties,as well as damage mechanism have been gained.At the same time,several corresponding standards and local regulations were established.However,the tensile fatigue property of SFRC hasn't been studied adequately.In this thesis,an axial tensile fatigue experiment was conducted.Data gained from the test were analyzed by statistical methods,thus the characteristics of failure,fatigue life curves and regularity of strain increase of SFRC under tensile fatigue loads were obtained.Specifically,this thesis includes the followings:(1)Three mixture proportions with different steel fiber content(0.5%,1% and 1.5%)of SFRC were designed,and the corresponding specimens were tested under static load.Data gained from this test were analyzed using the theory of fiber reinforced composite to study how will steel fiber content influence on SFRC's mechanical property.Take both workability and mechanical property into consideration,1.5% was recommended as the best steel fiber content for SFRC.(2)Based on the static load test described above,an axial tensile fatigue experiment was conducted,in which 52 prismatic specimens were tested under various stress conditions.SFRC's fatigue life values gained from the test were proved to be in well agreement with Weibull distribution and normal distribution,while the former distribution performs better than the latter.Thus a series of fatigue life equations under different survival probabilities were established,as well as the ultimate fatigue strength equation containing two parameters—the ratios of maximum and minimum stress to tensile strength.(3)Comparing SFRC's fatigue life equations to that of ordinary concrete,it shows that SFRC's tensile fatigue life under all kinds of stress conditions is apparently higher than the latter's.This improvement is most significant when the value of the ratios of maximum stress to tensile strength is between 0.7 and 0.8,which can reach 10~20 times.Besides,SFRC is more sensitive to stress amplitude.(4)The tensile fatigue life history-maximum strain curve of SFRC gained from this test was compared with that of ordinary concrete.Both the two kinds of curves have similar variation trend,but the proportions of each variation stage are different.