| Fiber reinforced concrete,as a new building material,has been widely used in domestic and foreign projects.Polypropylene fibers with the advantages of low density,low price,easy dispersion and stable chemical properties have broad engineering application prospects.In this paper,two kinds of polypropylene fine fibers and one size of polypropylene crude fiber were selected and blended into concrete in a certain proportion.Through the normal section bending test and shear test of oblique section,the load-span deflection curve,crack load size,crack shape and failure mode of concrete beams under different fiber content were deeply compared and analyzed.The influence of multi-scale polypropylene fibers on flexural and shear capacity of concrete beams had been analyzed.The multi-scale polypropylene fiber reinforced concrete beams were loaded and analyzed by ABAQUS software,and the numerical simulation results and experimental results had been compared.The control group with different fiber content was designed to carry out numerical simulation experiments to study the influence of different fiber content on the flexural and shear strength of concrete beams.Based on the results of numerical simulation and experimental data,the formulas of ultimate flexural and shear capacity of multi-scale polypropylene fiber reinforced concrete are modified by using composite material theory.The main contents and research results of this paper are as follows:(1)The influence of polypropylene fiber on the compressive strength and splitting tensile strength of concrete was studied through the compressive strength and splitting tensile strength tests of polypropylene fiber reinforced concrete.The results show that different sizes of fibers can play different roles in different stages of concrete compression.Polypropylene crude fibers mainly inhibit the expansion of macro-cracks,fine fibers mainly inhibit the formation and development of cracks at the initial stage of compression.And multi-scale polypropylene fibers can play a synergistic role,significantly inhibiting the toughening effect and improving the compressive strength and splitting tensile strength of concrete.(2)The effects of multi-scale polypropylene fibers on cracking load,mid-span deflection,crack morphology and failure mode of reinforced concrete beams were studied by means of bending tests of normal sections of reinforced concrete beams.The results show that the multi-scale polypropylene fiber can improve the cracking load of concrete beams,inhibit the development of cracks,and increase the integrity and ductility of beams.Compared with plain concrete beams,the flexural ultimate bearing capacity of multi-scale polypropylene fiber reinforced concrete beams tested in this paper increased by 11.95%.(3)Through the oblique section shear test of multi-scale polypropylene fiber reinforced concrete beams,the effects of multi-scale polypropylene fiber on the cracking load,mid-span deflection,crack morphology and failure mode of concrete beams under shear were studied.The results show that the multi-scale polypropylene fiber can play a significant role in crack resistance and toughening,enhance the ductility of concrete,and improve the brittle shear failure mode of concrete beams.Compared with plain concrete beams,the shear capacity of multi-scale polypropylene fiber reinforced concrete beams increased by 17.07%.(4)Using ABAQUS finite element software,the loading simulation of positive section bending test and oblique section shear test of multi-scale polypropylene fiber concrete beams had been carried out,and the load,deflection,stress and concrete tension-compression damage of concrete beams had been compared and analyzed by finite element analysis and test.The control group of concrete beams with different fiber content was designed,and the simulation test was carried out to study the effect of different fiber content on the bending and shear properties of concrete beams.The results show that the numerical simulation results are basically consistent with the experimental results.The addition of multi-scale polypropylene fibers can significantly enhance the flexural and shear toughness of concrete beams,improve the deformability of beams,and enhance the ultimate bearing capacity of beams.Combining with the Code of Concrete Structure Design,the formula is modified on the basis of the theoretical formula of flexural capacity of concrete beams.The fiber reinforced coefficient of the formula for calculating shear capacity of fiber reinforced concrete beams is revised by using composite material theory.The theoretical value has been compared with the test value to evaluate the applicability of the formula is evaluated,which provides a theoretical basis for engineering practice. |
