Analysis Of Stressing State Characteristics Of Concrete Filled Steel Tubular Circular Arch Under Radial Uniform Loads

In deep soft rock roadway,the concrete-filled steel tubular(CFST)supports are often used as the supporting structure,which are usually made of multi-segment CFST circular arches,and the research of this kind of circular arch is lagging behind its application.The bearing capacity of the arch can not be calculated accurately,and the general working law as well as the conservative degree of the application are not revealed.In view of this problem,based on the theory of structural stress ing state,this paper analyzes the stressing state characteristics of the CFST circular arch by modeling the strain data,revealing the general working law and providing the basis for accurately predicting the bearing capacity of this kind of CFST circular arch.(1)Firstly,the strain data are transformed into the generalized strain energy density(GSED)values,for establishing the stressing state modes and characteristic parameters of the CFST circular arch and its sub-parts(steel tube and confined concrete).Then,the Mann-Kendall criterion is used to detect the mutation points(characteristic loads)in the evolving curve of characteristic parameters with the load increase.The rationality of these characteristic loads is verified by the corresponding evolution and mutation characteristics in the structural stress ing state modes and submodes,which revealed the general working law of the CFST circular arch and its sub-parts.(2)According to the characteristic point of stressing state,it defines the starting point at the failure process of CFST arch,and refines the failure load by this point;At the same time,it also defines the linear-elastic branch point,elastic-plastic branch point and progressive failure point of the CFST arch.Furthermore,it analyzes the quantitative or qualitative change characteristics of the stress ing state near the characteristic load points.(3)The stressing state of the CFST circular arch under different parameters(wall thickness of steel tube,diameter of steel tube,rise span ratio,concrete strength grade,steel fiber content in confined concrete and diameter of strengthened steel)is analyzed.Then,the stressing state characteristic parameters,characteristic loads and stressing state modes of the sub-parts(steel tube and confined concrete)of the arch are contrasted under the condition of single parameter changing.The analysis and contrast results present that these parameters mainly affect the bearing capacity and the failure process.(4)The state configuration interpolation method is used to calculate the axial force of the composite section,steel tube section and confined concrete section on the mid-span section of the arch.Through the analysis of the axial force,it is found that the axial force of confined concrete begins to play a control role from the elastic-plastic branch load of the arch.Based on the results of stressing state analysis,it is proposed that the elastic-plastic branch load can be directly used as the design load of the arch,which are compared with the design value of the relevant design code.The comparison results show that the bearing capacity of this kind o f member can be used to a greater extent in the design according to the elastic-plastic branch load,which can provide a reference for the engineering practice.