Research On Performance Of Crack Arresting And Calcution Method Of Crack Width Of Steel Fiber Reinforcement Concrete Segment

Cracks are one of the most common diseases of shield lining segment linings.Cracks occur during the production and construction of segments and during the operation of the tunnel.Cracks not only affect the overall safety of the structure,but also easily induce groundwater leakage and other durability problems.The cracks can be suppressed by adding steel fibers,but the research on performance of crack arresting of steel fiber reinforced concrete segments under load is less.Therefore,in this thesis,many methods such as literature research,basic mechanical test,small scale model test and full scale model test were used to research the performance of crack arresting and crack width calculation method of steel fiber reinforcement concrete.The main research work and conclusions are as follows:（1）The experimental results of the mechanical properties of steel fiber reinforced concrete show that the addition of steel fiber has no obvious effect on the compressive properties and flexural tensile strength of concrete.However,the splitting tensile strength and the residual bending tensile strength have a better promotion effect,and the splitting tensile strength increases with the increase of steel fiber content,the maximum increase is 95.3%.（2）The small-scale model of steel fiber reinforcement concrete with three-point bending beam and eccentric loading columns were studied.It is found that the steel fiber has no effect on the trend of the continuous growth of crack width of reinforced concrete,and the crack arresting coefficient will gradually approach a stable value with the development of crack width;the crack arresting coefficient of three-point bending beam with the dosage of 30kg/m³and 35kg/m³ is 0.749 and 0.885 respectively,and the crack resistance coefficient of the eccentric loading columns with the dosage of 30kg/m³ and 35kg/m³ is 0.682 and 0.747respectively.（3）Based on the research of the crack width and crack spacing of the full-scale model of steel fiber reinforcement concrete（segment,compression-bending beam and dip angle beam）,it is found that:the addition of steel fiber and the increase of reinforcement ratio can effectively reduce the crack width and the performence of crack arresting will be better with the increase of the dosage of steel fiber;the crack arresting coefficient of the type and the dosage of 4D-30kg/m³,4D-25 kg/m³,5D-25 kg/m³ is divided 0.7,0.88 and 0.5 respectively.For the crack spacing,the cracks of steel fiber reinforcement concrete are obviously denser than that of reinforced concrete,and the dosage and type of the fiber have no significant influence on the average crack spacing.The average crack spacing is 0.5-0.6 times of reinforced concrete,and the maximum crack spacing is 0.6-0.7 times of reinforced concrete.（4）The calculation model of crack width of steel fiber reinforcement concrete was put forward.By considering the tensile effect of concrete in tension area and the effect of concrete in compression area under large bias pressure,the calculation method of steel stress was further optimized,and the calculation formula of average strain difference was finally obtained by referring to relevant standards.The calculation values of maximum crack spacing of various codes are analyzed and compared with the test results,The results show that the ratio of the maximum crack spacing to the minimum crack spacing is 2.2～2.8,and the ratio of the maximum crack spacing to the average crack spacing is about 1.5.The empirical coefficients K₁ and K₂ in the calculation of the maximum crack spacing are 1.5*1.9 and 2.8/4,respectively.（5）Combined with the full-scale model test,the safety analysis of the calculation model was carried out.The maximum crack spacing calculation ratio of the calculation model is1.107.Most of the final crack width calculation results are larger than the test value.And the safety factors of dip angle beam,segment and compression-bending beam are between 2-3,1-2 and 1 respectively.In addition,the calculated results based on the design conditions meet the design requirements,and when the 4D steel fiber content is 30kg/m³,the calculated values of some design conditions（such as condition 1,3 and 5）are smaller than the original design reinforced concrete calculated crack width,which further proves the feasibility of the steel fiber reinforcement concrete.