Analysis Of Fracture Energy And Size Effect Of Steel Fiber Reinforced High-Strength Concrete

Size effect is a common property of quasi-brittle materials,and fracture parameters of concrete also have a size effect as a quasi-brittle material.Fracture energy is an important index of fracture performance for concrete.Due to the size effect,the concrete fracture energy is not a constant,and the actual reflection of the true fracture energy of the concrete is very important.It is not only important for studying the concrete material itself,but also has an important guiding role for the concrete structure design.According to the above problems,a total of 156 high-strength concrete SENBs of different sizes,span-to-depth ratios and crack-to-depth ratios were subjected to the three-point loading test as recommended by the International Union of Laboratories and Experts in Construction Materials,Systems and Structures(RILEM).On this basis,the influence of steel fiber on the fracture energy and size effect of concrete was considered.The main contents are as follows:(1)When the added steel fibers amount reach 2%,the compressive strength and the splitting tensile strength of steel fiber reinforced high-strength concrete increased by 27.8%and 171.8%respectively compared with that of the reference concrete.When the added steel fibers amount reach 3%,the effect of steel fiber on the compressive strength and the splitting tensile strength of high-strength concrete was slightly weakened compared with steel fiber content of 2%,but the compressive strength and the splitting tensile strength of steel fiber reinforced high-strength concrete increased by 25.3%and 123.5%respectively compared with that of the reference concrete.(2)The addition of steel fiber to concrete can significantly improve several fracture parameters(i.e.,experimental test fracture energy Gf,the fracture energy GF unaffected by size,the boundary influence length al*,the initial fracture energy G'f and the fracture toughness KIC),which in turn influence the size effect on the fracture energy of high-strength concrete.(3)In BEM,there is an obvious linear correlation between test fracture energy Gf with different steel fiber contents and the fracture ligament length(W—a).Based on the bilinear distribution model of the local fracture energy gf,the relationship among the experimental test fracture energy Gf,the local fracture energy gf,and the fracture energy unaffected by specimen size GF can be established through testing,and the fracture energy unaffected by specimen size GF can be determined based on the experimental test fracture energy Gf.These relationships allow laboratory small-size SENB specimens to be used for analyzing the influence of steel fiber on the fracture energy unaffected by specimen size GF.(4)According to the SEL,as the steel fiber content increases,the initial fracture energy G'f versus the fracture energy unaffected by size GF decreases and the fracture behavior of high-strength concrete gradually approaches strength criterion.The addition of steel fiber can reduce the size effect on the fracture energy of high-strength concrete.However,some steel fiber contents cause the values of ?A,?B,m in the SEL to exceed the range specified by RILEM,which reduces confidence in the accuracy of linear regression results.