The Mechanical Behaviour Of Concrete-filled Non-uni-thickness Walled Rectangular Steel Tubular Members

As a new kind of composite section,the rectangular concrete-filled non-uni-thickness walled steel tubular(CFST)members can take full advantage of material strength to improve the bearing capacity of members by the optimization design of cross-section.In this paper,the mechanical behavior of rectangular non-uni-thickness walled CFST members has been discussed by experimental study,numerical calculation and theoretical analysis,which is mainly composed of the following aspects.First,the flexural behavior of rectangular non-uni-thickness walled CFST members is studied.7 flexural members are tested in this paper.The results indicate that the smaller the thickness ratio of the upper flange to bottom one is,the more concrete working in the ultimate state there is,which means the flexural behavior of composite cross-section is better.The fiber model method and the finite element method are used to simulate the whole process of tests,the results of which match well with tests.The analytic expression of bending capacity of rectangular non-uni-thickness walled CFST sections is derived and the optimization problem of bending members is discussed.Especially for high steel ratio and high strength concrete members,optimal section design can improve the bearing capacity remarkably.Then,the study of the bearing behavior of rectangular non-uni-thickness walled CFST slender columns is carried out.The test results of 4 axially loaded slender columns and 8 eccentrically loaded slender columns show that under the same steel ratio,slenderness ratio and eccentricity,non-uni-thickness walled columns have greater bearing capacity than uni-thickness walled columns.The numerical simulation results of the fiber model method and the finite element method also indicate that under certain steel ratio,slender ratio and eccentricity,the bearing capacity of rectangular non-uni-thickness walled CFST eccentrically loaded slender columns can improve 57% than that of uni-thickness walled CFST columns at most.The results indicate that rectangular non-uni-thickness walled CFST sections can significantly improve the bearing capacity of eccentrically loaded slender columns.The analytic expression of stability bearing capacity of rectangular non-uni-thickness walled CFST slender columns is derived,the results of which match well with the test results.Finally,the mechanical behavior of rectangular non-uni-thickness walled CFST stub columns is discussed.10 eccentrically loaded stub columns are tested,the results of which show that stub columns have great bearing capacity and ductility.The whole experiment process of eccentrically loaded stub columns is simulated by finite element method.The analytic expression of bearing capacity is derived and the corresponding parametric study is carried out in this paper.The results show that under the certain steel ratio and eccentricity,the bearing capacity of rectangular non-uni-thickness walled CFST eccentrically loaded stub columns can improve 17% than that of uni-thickness walled columns at most,which means optimal section has higher bearing potential.