Experimental Study And Numerical Simulation Of Mechanical Properties Of Steel Fiber Reinforced Concrete

Steel fiber reinforced concrete(SFRC)has better tensile,flexural,impact resistance,toughness and durability than traditional concrete.Previous researches on mechanical properties and structural design optimization of SFRC have been carried out.With the improvement of production and living standards,the development of SFRC not only needs to meet the strength requirements of safety and reliability,but also needs to develop in the direction of reducing costs and improving economic benefits.For example,the application of SFRC in shield segment can reduce the amount of reinforcement and control the development of cracks,and the application of steel fiber concrete to the construction of goaf retaining wall in coal mine will bring great economic benefits because of improving the toughness of retaining wall.With the rapid development of computer science and technology,qualitative analysis of mechanical properties of SFRC and its applied engineering structures by means of numerical simulation and artificial neural network will greatly reduce repetitive test activities,so as to promote and apply materials and structures scientifically.In this paper,the mechanical properties of SFRC are systematically studied by means of laboratory test,numerical simulation and full-scale test.Firstly,the mechanical properties of hooked-end steel fiber in concrete are studied qualitatively and quantitatively,the concept of end hooked-end angle is proposed,the influence of hooked-end angle,length-diameter ratio and dosage on mechanical properties of SFRC is explored,and the calculation formula of SFRC bending strength considering end hooked-end angle is proposed.Secondly,the CDP constitutive model is modified based on the constitutive model suggested by Model Code2010,and a VUMAT subroutine is written in FORTRAN language to carry out secondary development of material properties of nonlinear finite element simulation software,and the modified constitutive model is applied to numerical simulation.Combined with BP artificial neural network optimized by GA,it has been successfully verified in SFRC basic mechanical test and bending test.Finally,the hooked-end steel fiber is applied to shield segment,and the mechanical properties and failure mechanism of SFRC segment made by removing partial steel bars or all steel bars by steel fiber are systematically studied by combining the full scale test of segment with the numerical simulation of the new constitutive model,which enrich the theory of mechanical properties and structure of hooked-end type SFRC segment.The main research work of this paper is divided into the following four aspects:(1)For SFRC mixed with hooked-end steel fiber,the research idea considering the influence of hooked-end angle was proposed.Through the study of SFRC mixed with different content,different length-diameter ratio and different hooked-end angle,the compressive,tensile and flexural properties were studied.The results show that the compressive strength,tensile strength,elastic modulus and flexural strength of SFRC increase with the increase of hooked-end angle of steel fiber,length-diameter ratio of steel fiber and steel fiber content.It is found that the content of steel fiber is the key factor affecting the mechanical properties of SFRC,and only when the hooked-end angle of steel fiber changes within a certain range,the increase of steel fiber aspect ratio will affect the flexural properties of SFRC.(2)Through four-point and three-point tests on SFRC,the calculation formula of flexural and tensile strength considering the hooked-end angle was proposed,and the calculation formula was verified by the verification test,the error was less than 6%,indicating the correctness of the formula.Combined with numerical simulation,VUMAT subroutine was written to develop the modified CDP constitutive model and simulate four-point and three-point tests of SFRC beam.The results show that the stress,deformation,tension and compression damage cloud graphs obtained by numerical simulation are in good agreement with the physical test,and the load-deflection curves obtained by simulation are well matched with the load-deflection curves obtained by test.(3)Mechanical properties of SFRC were studied by artificial neural network.Firstly,the nonlinear relationship between steel fiber parameters and mechanical properties of SFRC was established based on the BP neural network optimized by GA.Then,the mechanical properties and constitutive model of SFRC with different steel fiber parameters were predicted by neural network,and the predicted R~2was greater than 0.9.Finally,the bending performance of SFRC was studied by combining numerical simulation with GA-BP neural network prediction model.The results show that GA-BP neural network processing and classification of a large number of data makes the influence of different steel fiber parameters on the mechanical properties of SFRC more significant,which verifies that the mechanical properties of SFRC increase with the increase of steel fiber parameters,and provides theoretical guidance and reference significance for using artificial neural network to study the related parameters and properties of SFRC.(4)Combined with the influence of hooked-end steel fiber on mechanical properties of SFRC,the application of hooked-end steel fiber in engineering structure was studied.Firstly,SFRC shield segment with steel fiber partially or completely replacing steel bars was made.Then,full scale tests of bending resistance and concentrated load pushing were carried out to observe and record the deformation of the segment.Finally,the modified CDP constitutive model was used to simulate the SFRC segment.The results show that in normal conditions,SFRC segment made by removing all steel bars by steel fiber can be used,and its resistance to deformation and external load is similar to the SFRC segment made by removing partial steel bars by steel fiber.At the same time,the steel fiber improves the crack resistance of the SFRC segment.However,the bearing capacity of SFRC segment made by removing partial steel bars by steel fiber is stronger,and numerical simulation and full-scale test verify each other.The research results provide a theoretical basis for the design and application of SFRC segments.