Study On Mechanical Properties And Model Test Of Concrete Filled Steel Tubular Arch Frame

Underground poured concrete-filled steel tubular support(CFST),which is a kind of new supporting technology for soft rock roadway in coal mines.This paper is to study the deviation law of neutral layer in the cross section and bending failure mechanism of arch-shaped CFST member under the uniformly distributed radial load which considered the ends slip by the experiments,numerical simulation and theoretical calculated analysis.Based on the lots of the CFST short columns under single loading and CFST circular arches under six-point even loading condition were designed and tested thoroughly,three-point non-equal division uniformly distributed radial loading tests and six-point equal division uniformly distributed radial loading test,four-point equal division uniformly distributed radial loading tests and indoor model similar simulation test of CFST arch centering,the working mechanisms of the CFST short columns under axial compression,the working mechanism and bending mechanical performance of the CFST circular arches with different diameter-thickness ratio,ends slip moment and pressure layer thickness were researched.Also with failure analysis and control mechanisms of round roadway under different support conditions?Which promote the development of supporting technology of the support,which has important theoretical significance and practical value for the soft rock roadway retaining.(1)Based on the existing damage analysis model,an analytical model for the constitutive relation of the bond interface with the damage evolution method which is proposed based on the non-thickness cohesive bond eleemnt in ABAQUS.This finite analysis method uses the three-dimensional numerical simulation on the core concrete of concrete filled steel tube(CFST)short clumn,which combines with test for uniaxial compressive strength which displayed accurately in the whole progress of uniaxial compression experiment.The actual experiment results showed that the suitable load-displacement curve of the core concrete specimen,which reflects the load-slip relationship and strain distribution in the process of peeling failure of core concrete.And there is no influence on the bearing capacity of the overall core concrete in the finite analysis,which proved the efficiency of the proposed model and method.The load slip curve obtained by the finite element analysis is in good agreement with the analytical model and the experimental results,and and the basis for the study of other components of CFST structures.(2)Then,through the three-point uniform load and non-uniform load conditions,the displacement of the CFST at the mid-span position and the strain and ultimate bearing capacity of the outer wall of the steel tube are analyzed.The arc-arch specimens with different aspect ratios and ultimate bearing capacity are analyzed.Ability to analyze and explore the migration law of the neutral layer position.The experimental results and simulation results show that the fixed-section CFR circular arch specimens at both ends are damaged by the triple action of tension and compression at the arch,and the core concrete is cracked.As the load continues to increase,the existence of cracks leads to concrete.The volume expands,which in turn causes the steel tube to bulge.Through laboratory tests and numerical simulations,as well as the results of on-site monitoring,it can be seen that the zero point of the cross-section strain value of the circular arch span corresponds to the neutral layer position,and the neutral layer position shifts upward with the load increase first,and there is a significant offset turning point;After the turning point,the position of the neutral layer shifts to the lower part of the section as the load increases;the position of the neutral layer close to the load extreme tends to be stable and is no longer offset.(3)Through monitoring the displacement and different slip amount on the position of the middle across section and arch foot of the concrete filled steel tube(CFST)arch under the condition of 6 points uniform loading,the strain and the ultimate bearing capacity of outer steel pipe and inner core of concrete are analyzed.Meanwhile,a kind of cohensive element without thickness which had been combined with the constitutive model of concrete was applied for the three-dimensuonal simulation analysis of bending process in ABAQUS,which displayed accurately in the whole progress of uniaxial compression experiment.The actual monitoring and experiment results shows that the CFST arch was damaged under the influence of triple action of pulling,pressing and bending,and some cracks appeared on the process of arch foot's sliding,which is different from the condition of two fixed ends of the CFST arch.When the loading increasingly,the presence of cracks leads to concrete volume expansion,and then make the steel tube drum package.In the range of a certain amount of arch foot slippage,the bending moment of the middle section of core concrete and arch foot are both increased dramatically,the core concrete bottom is tensiled while the top is under pressure,moreover,the bearing capacity of the CFST arch is decreased with the increase of the amount of slip of arch foot.Through the laboratory test and numerical simulation,as well as the results of field monitoring,it is found that can be seen which means the displacement of the middle section of the CFST arch was twice times of the amount of slip on both arch ends.After reaching the ultimate load the yield of CFST circular arch is one of the hoop action failure of the concrete.Not only the boundary condition of different slip amount in CFST arch foot can lead a better understand the mechanical properties of CFST,also there is a certain engineering guidance significance to the CFST construction condition of roadway.(4)Through the monitoring of the deformation of the middle section and the left-right side section in the concrete filled steel tube(CFST)stent with the condition of uniform loading,which combined with ABAQUS for simulation analysis of bending process with cohesive elements the main research method in the constitutive model of concrete.This finite analysismethod uses the three-dimensional numerical simulation which displayed accurately in the whole progress of uniaxial compression experiment with CFST short column and core conrete test block in the micro aspects.The actual morniting analysis shows that the bearing capacity of the support stent increases with the gathering of the thickness of the middle section and left-right side section in the range of a certain thickness for the letting pressure layer,which weaken the axial force of the support stent in the CFST arch and decreased with the deformation and destruction tempo of core concrete in the CFST stent.There are some cracks appeared on the process of pressing,when the loading increasingly,the presence of cracks leads to concrete volume expansion,and then make the CFST short column drum package.After reaching the ultimate load the yield of CFST circular arch is one of the hoop action failure of the concrete.Not only the boundary condition of different layer of the CFST support stent can lead a better understand the mechanical properties of CFST,also there is a certain engineering guidance significance to the non-dense pressure construction condition.