| The application of unreinforced steel fiber concrete in subway projects effectively enhances the mechanical properties of the structure and the residual strength after cracking,and solves the problems of excessive self-weight and easy cracking of corners due to the rebar-overuse.The incorporation of steel fibers also improves the overall durability of the tube segments,saving a lot of maintenance costs.This research aims to solve the problem of the lack of calculation methods for unreinforced steel fiber concrete in engineering design applications.According to the load situation of the supporting project,it passes the unreinforced steel fiber concrete mechanical performance test,toughness test,full-scale segment compression test,and section stress.State assumptions,theoretical derivation and other methods put forward the ultimate state design calculation method of the unreinforced steel fiber concrete segment bearing capacity based on the limit state design method,and compared with the full-scale segment compression test value and the European standard Model Code theoretical value It proves the rationality and advancement of the optimized calculation method.The main results of the comprehensive full text are as follows:1.Analyzing the basic mechanical test of unreinforced steel fiber concrete shows that:the increase of the steel fiber content under the same mix ratio can effectively improve the compressive strength of the test piece,and the mix ratio CQ is adjusted for the 30kg/m3 steel fiber concrete test piece.Because CQB can significantly improve the compressive strength,the change of the mix ratio has almost no effect on the 40kg/m3 sample.In the notched beam test,the steel fiber concrete specimens under three conditions belong to the category of softening model.The optimization of the mix ratio also significantly helps to improve the flexural and tensile performance of the notched beam.The increase of the steel fiber content will directly affect the flexural and tensile strength of the component.2.In the full-scale test of steel fiber concrete segment compression and bending,the displacement of the segment gradually increases steadily after the initial crack,and the rate increase increases until the specimen fails to stop loading.When the final failure occurs,the maximum measured value of the displacement on one side of the main crack can reach 10～15mm,and the difference of the displacement on both sides of the mid-span is between 4～6mm.The initial cracks all appear on the inner arc surface of the segment,near the vertical loading point;the fracture is accompanied by the peeling of the skin and internal aggregate of the segment,and the steel fiber in the tension zone is mainly pulled out.By calculating the fiber dispersion coefficient,it can be known that the steel fiber in the CQ30 segments are well dispersed,which can ensure the reliability of the remaining test data and results.3.According to the test data and failure form of the notched beam,an optimized constitutive model for unreinforced steel fiber concrete is proposed,and the equivalent tensile strength calculation formula is proposed.The eccentricity range and bearing capacity calculation method of unreinforced steel fiber concrete under full-section compression are proposed,and the boundary compression zone height is defined to distinguish large and small eccentricities,and then specific calculation methods are proposed respectively,forming a complete ultimate state design calculation method of the unreinforced steel fiber concrete front section.4.By traversing the height of the cross-section compression zone in the optimization design method,the ultimate state M-N curve of the segment bearing capacity of the optimization design method is obtained and compared with the segment bending test value and the theoretical value of the Model Code to find the theory of the optimization calculation method.The similarity between the value and the bearing capacity of the segment in the full-scale test can reach more than 95%.Compared with the theoretical value in Model Code,the accuracy is improved by 12.4%～33.5%,which verifies the rationality of the optimized design method. |
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