| The Reinforced Concrete-Filled Steel Tube structure as a new type of structure,has been widespread application in Bridges and ports.It’s the same principle as ordinary reinforced concrete pile is poured into the steel tube,and Reinforced Concrete-Filled Steel Tube added with longitudinal and stirrup,but there are few studies on this new structural form,and there is no systematic specification about it now.Therefore,this paper will study the failure modes and mechanical properties of Reinforced Concrete-Filled Steel Tube.Taking the two stage pile foundation of the orchard as the prototype,the thickness of the steel tube,the reinforcement ratio and the hoop ratio as variables,this paper have carried out the axial compression test of 6 Reinforced Concrete-Filled Steel Tube short columns and 2 Concrete-Filled Steel Tube short columns.This paper takes the orchard second-stage pile foundation as the prototype,and the steel casing thickness,reinforcement ratio and stirrup ratio are variables.The test results show that the steel tube and the stirrup have a restrain effect on the core concrete in the steel-reinforcement concrete structure,and the double restraining effect is obvious.The restrain effect can effectively restrain the development of concrete cracks,which makes the steel retaining tube have higher bearing capacity and plasticity than the traditional Concrete-Filled Steel Tube.When the steel tube has sufficient restraining effect,the steel tube,concrete and longitudinal are all yield when the specimen is destroyed,and the material properties are fully utilized.Based on the ABAQUS finite element software,the steel tube thickness,reinforcement ratio,stirrup ratio as the parameters,analyzes the one ordinary reinforced concrete short column and nine Reinforced Concrete-Filled Steel Tube short column,the validity of the model is verified by comparison with the experimental results.The results show that the restraining effect of Stirrup on core concrete has significant influence on the bearing capacity,plasticity and ductility of Reinforced Concrete-Filled Steel Tube short columns under axial load,with the decrease of the stirrup spacing,the bearing capacity and ductility of the specimen are improved obviously.However,after the stirrup spacing is less than 140 mm,the bearing capacity and ductility performance have no obvious improvement.Based on indoor physical model test and ABAQUS finite element analysis of Reinforced Concrete-Filled Steel Tube structure,the internal force distribution rule of Reinforced Concrete-Filled Steel Tube short columns under axial compression is analyzed by the method of stripping analysis.In the plastic stage,the steel tube longitudinal axial force decreased,internal force transferred to the core concrete core gradually and the concrete performance is greatly improved under the two-way constraint of steel tube and stirrup,the the combined strength is about 1.59 times of the standard strength of concrete.At the same time,base on the "unified theory" and "limit equilibrium theory" of Concrete-Filled Steel Tube,this paper derived the compression stiffness and ultimate bearing capacity formula of Reinforced Concrete-Filled Steel Tube structure under axial pressure,and the error is small compared with the the test results.Reference "The regulations of structural design and construction of concrete filled steel tube","Steel structure design specification","Concrete structure design code","Steel structure engineering construction quality acceptance specification",“Concrete engineering construction quality acceptance specification” and other specifications,this paper summarizes the simple design regulations and construction precautions of Reinforced Concrete-Filled Steel Tube.Based on the formula of axial pressure of Reinforced Concrete-Filled Steel Tube short column,the reasonable ratio of diameter to thickness is derived.After determine longitudinal reinforcement and stirrup,That can obtain the confining coefficient of steel tube,and then obtain the thickness of steel tube. |
