Study On Serviceability Limit State Design Method Of Steel Fiber Reinforced Concrete Segment

Steel fiber reinforced concrete is widely used in engineering structures due to its excellent crack arresting,anti-permeability and durability,at present,however,steel fibers do not completely replace steel bars in concrete components.On the one hand,the excellent characteristics of steel fiber have not been fully played,on the other hand,the cost of construction has not been reduced.On the contrary,a large number of funds is going to be put into the construction process.In fact,some special space can be used steel fiber reinforced concrete components.Relying on the Shenyang Metro Line 9,literature surveys,mechanical tests,bending beam member tests,and theoretical deductions has been adopted in this paper to study on the design method of serviceability limit state of steel fiber reinforced concrete segment under different stress conditions,and the following main results are obtained:(1)The influence of steel fiber on the mechanical properties of concrete matrix has been studied through 12 cube compression tests and 48 notched beam tests.The experimental results show that the cube compressive strength is increased by 10%~18%because of the addition of steel fibers.For 4D steel fiber reinforced concrete,the best mixing amount is35kg/m~3.For 5D steel fiber reinforced concrete,the best mixing amount is 30kg/m~3.The softening model is the main constitutive relation of 4D and 5D steel fiber reinforced concrete when 25~40kg/m~3 content is added.(2)The influence of stress condition on the bearing capacity of steel fiber reinforced concrete members is studied through the experiments of bending beam members under different eccentricity conditions.The results show that when the width of the main crack is0.2mm,the bending moment bearing capacity of the eccentricity e=0.10m is 1.5 times,2.25times and 2.5 times of the bearing capacity of the eccentricity e=0.15m,e=0.20m and e=0.30m,respectively.In addition,the relationship between the height and width of the main crack of the bending beam is fitted by Boltsmann.The results of the prediction fitting formula and the test results are compared to find that the fitting results are reliable.(3)Because it is difficult to directly calculate the crack width of unreinforced concrete members at present,a set of serviceability limit state design method based on the expression of bearing capacity is proposed.On the basis of experiments,comparing and analyzing the limitations and shortcomings of the design methods at home and abroad,with the reference envelope line method and considering the rational distribution of stress and strain in the cross section,the design method under different eccentricity is put forward.And its rationality is verified by the typical engineering conditions.(4)By means of gradient optimization method and MATLAB programming algorithm,the reliability analysis of steel fiber reinforced concrete segments with different eccentricity is realized.The calculation results show that the smaller the eccentricity,the greater the reliability index of the unreinforced steel fiber reinforced concrete segment,the more reliable the material,and the better the applicability of the design method are.