Mechanical Analysis Of Concrete Filled Steel Tubular Columns Based On Thick-walled Cylinder Theory

Concrete-filled steel tubular column is more popular in construction and bridge engineering due to its improvement of bearing capacity,ductility and seismic performance.However,the force of concrete-filled steel tubular column is complicated and the research about concrete-filled steel tubular column needs to be studied intensively.When studying the bearing capacity of concrete-filled steel tubular column,round steel tubes can be assumed as thick-walled cylinders.At the same time,many problems in engineering that can also be simplified to thick-walled cylinders,such as pile foundation reaming,tunnel and supporting structure.Once these structures are destroyed,some harmful consequences would be happened.Hence,it is necessary to more accurately study the ultimate bearing capacity of the structures.And effectively increasing the ultimate bearing capacity is also important.There are many materials that the yield strength and elastic modulus are different when they are in the states of tension and compression.Previous studies have shown that both of states have significant impacts on the ultimate internal pressure,but only one aspect is considered.And most of yield criterions only apply to a certain type of material.Therefore,the single and double layered thick-walled cylinders were taken as the research object to study the stress distribution and ultimate bearing capacity.The specific research contents are as follows:(1)Based on the twin shear unified strength theory and the ideal elastoplastic constitutive model,the stress distribution of the single-layered thick-walled cylinder in the elastic zone and the plastic zone was derived by considering the effects of the intermediate principal stress effect,the different yield strength and tensile modulus in tension-compression as well as the elastic,plastic and shakedown limit internal pressure solutions of the structure were solved.The correctness of the theoretical calculations in this paper was validated by the degradation solutions,experimental results and numerical simulation results.The effects of the ratio of outer radius to inner radius,the unified strength theory parameter,the tension-compression strength ratio and the tension-compression modulus coefficient on the various limit solutions were analyzed.(2)Considering the influence of different properties of elastic modulus in tension and compression,the stress field,elastic and plastic limit internal pressure of a double-layered thick-walled cylinder made of ideal elastic-plastic materials under uniform internal pressure were deduced by using the twin shear unified strength theory.The effects of wall thickness,layering radius,unified strength theory parameter,ratio of tensile to compressive strength,and the tension-compression modulus coefficient on ultimate solutions were analyzed.elastic and plastic limit internal pressure solutions of double-layered thick-walled cylinder under uniformly distributed internal pressure were deduced by considering the influence of the characteristic of linear strengthening of materials,the stress distribution under elastic and plastic conditions.The relations between ultimate solutions and the coefficient of hardening modulus,the tension-compression strength ratio,the unified strength theory parameter,the wall thickness and the layering radius were analyzed.(3)The thick-walled cylinder theory is applied to the concrete filled steel tube column.The ultimate internal pressure and stress field of the circular steel tube under the elastic and plastic state were solved.The stress distribution of the core concrete was obtained according to the stress distribution analysis of the steel pipe.The axial compressive bearing capacity of the concrete filled steel tube column was derived according to the axial stress of the steel tube and the concrete.(4)Using finite element software ANSYS,the stress distribution of thick-walled cylinder under uniform internal pressure was simulated and calculated based on Mises criterion.The radius of plastic zone radius was obtained from the simulation results.The theoretically calculated solutions agree well with the simulation results and the correctness of the theoretically calculated solutions can be verified.