Study On Ultimate Bearing Capacity Of Large Diameter Concrete-filled Steel Tube Members

The concrete-filled steel tube arch bridge has been widely used in China due to its large bearing capacity,strong spanning ability and beautiful appearance.The maximum span of the concrete-filled steel tube arch bridge has reached 575 m,and a feasibility study has been carried out for the 700 m arch bridge.As the span of concrete-filled steel tube arch bridges gradually increases,larger-span arch bridges require concrete-filled steel tube members with a pipe diameter of 1.5m or more to meet the requirements for bearing capacity.However,the current standard is only applicable to the calculation of the bearing capacity of concrete-filled steel tube members with a diameter of less than 1.5m.Based on the above situation,this paper carries out finite element simulation analysis for the bearing capacity of concrete-filled steel tube members with a diameter of more than 1.5m.The main research contents are as follows:(1)Based on the constitutive relationship of steel and the constitutive relationship of core concrete,using ANSYS finite element program to establish a concrete-filled steel tube solid model with a pipe diameter of 1.5m～2.0m.This model will be used to analyze the bearing capacity of components with different pipe diameters,different material strengths and different ratio of steel.In order to verify the analysis results,the unified theory,limit equilibrium method and standard calculation formula will be used for comparison.(2)Based on the principle of equivalence of circumferential stress of steel pipes,the thermal expansion stress of axisymmetric shell elements is used to simulate the self-stress effect of concrete,and the relationship between concrete self-stress and temperature under different pipe diameters is established.According to the constitutive model of the selfstressing concrete-filled steel tube,the influence of the self-stress of 1MPa～5MPa on the bearing capacity of the concrete-filled steel tube member with a pipe diameter of1.5m～2.0m is analyzed.(3)For coronal voids and crescent voids,the surface-to-surface contact element is used to establish a bond-slip model for concrete filled steel tubes with a diameter of1.5m～2.0m.The influence of different void rates on the deformation trend,stress distribution and bearing capacity of concrete-filled steel tube members is analyzed.Regression analysis is used to obtain the calculation formulas for the reduction coefficients of the component bearing capacity corresponding to the two void forms.(4)The bearing capacity analysis of the concrete-filled steel tube member including the initial stress of the steel tube and the self-stress of the concrete is carried out.Using the space curved surface fitting method,a correction factor for the bearing capacity of members considering the effects of the initial stress of the steel tube and the self-stress of the concrete is proposed to expand the application range of the calculation formula for the bearing capacity of the concrete-filled steel tube in the current specification.In this way,the formula can be applied to the calculation of the bearing capacity of concretefilled steel tube members with a pipe diameter of 1.5m to 2.0m.