Circular Steel Tube Of High Strength Lightweight Aggregate Concrete Structure Mechanical Performance

This paper presents theoretical analysis deeply on the behavior of lightweight aggregate concrete filled circular steel tubular (LCFST) structures. Strength criterion and constitutive model for lightweight aggregate concrete under multi-axial stress states was proposed, the behavior of LCFST stub columns under axial compression was discussed, the theoretical models of LCFST under pure bending and LCFST middle long columns under axial compression were developed, and the LCFST structures were studyed by ABAQUS. The main contents are listed as follows:(1) Axial stress-stain relations of laterally confined lightweight aggregate concrete under axial compression and stress-stain relations of lightweight aggregate concrete under uniaxial stress states were proposed.The equation was determined basically based on the existing experimental data. Through analyzing large numbers of test results of uniaxial mechanical properties of various strength of lightweight aggregate concrete, the unified formulas for mechanical indexes and the unified method of uniaxial stress-strain relationship were proposed. Based on triaxial stress-strain relationship for concrete, the stress-stain relations of lightweight aggregate concrete under uniaxial stress states were proposed.(2) The elasto-plastic analysis method of LCFST stub columns under axial compression was proposed, and thus the mechanical properties of LCFST stub columns under axial compression was illustrated.Utilizing the axial stress-strain relations for laterally confined lightweight aggregate concrete under axial compression, based on continuum mechanics, the mechanical model of concentric cylinders of circular steel tube with lightweight aggregate concrete core was determined. The elasto-plastic analysis method of LCFST stub columns was proposed, and a computer program was developed. Through analyzing the behavior of LCFST stub columns, the effect of the parameters for LCFST were discussed.(3) Practical calculation formulas of load bearing capacity for LCFST stub columns and middle long columns under axial compression were proposed, and pracstical calculation methods of axial force-strain relations and moment-curvature relations for the composite section of LCFST were presented. Based on elasto-plastic analysis method, the numerical constitutive model for the lightweight aggregate concrete filled steel tubes was determined, the practical calculation formulas of composite axial stiffness and axial ultimate capacity for LCFST stub columns were proposed, and the practical calculation methods of axial force-strain relations for the composite section were presented.Based on plane section assumption, layered method was applied to calculate the moment-curvature relations for the composite section of LCFST, the practical calculation formulas of composite flexural stiffness, flexural capacity were proposed, and practical calculation methods of moment-curvature relations for the composite section of LCFST were presented. Fiber model method was applied to calculate the load-deformation relations of LCFST middle long columns under concentric loading, and the practical calculation formulas of load bearing capacity for LCFST middle long columns under concentric loading were presented. Good agreement is obtained between these predicted results and experimental results.(4) Numerical simulation LCFST columns under axial compression and steel-concrete composite beams through ABAQUS, the reliability of the elasto-plastic analysis method and fiber model method by the author were verified.For LCFST, thought the establishment of ABAQUS finite element model, The load capacity and load-deformation relations of the specimens were calculate. Combined with the test results by other researchers, the result of calculate for the reliability of the elasto-plastic analysis method, fiber model method, the practical calculation formulas was contrasted., It demonstrated that all kinds of analysis model is reliable in predicting the load versus deformation relationships; For steel-lightweight aggregate concrete composite beam, thought the establishment of ABAQUS finite element model, Simulation the load-strain relations of the composite beam and the slip curve of between lightweight aggregate concrete and teel beam, The analysis results are in good agreement with the experiment ones from references.