Research On Compressive Behavior And Reliability Of Round-ended Steel Tube-Filled Concrete Column

Research of CFST mainly in square and rectangular sections at home and abroad, specially shaped CFST is less. The advantages of specially shaped Steel Tube-Filled Concrete (CFST) are flexible section form, diverse node constructor and good seismic performance, which have been has been gradually applied in engineering. A large size round-ended CFST tower with single cable plane was used in Houhu Bridge in Wuhan, which is an innovative structure. For round-ended CFST design, how to calculate bearing capacity, the most basic and reliable research work is to study mechanical behavior through model experiment, combined with theoretical analysis to make for experimental data, and thus provide basis for structure design.Based on Houhu Bridge project, compressive mechanical properties of round-ended CFST are studied through axial compression experiments, eccentric compression experiments and finite element analysis. Based on reliability theory, reliability of round-ended CFST tower is studied by reliability analysis module of ANSYS. The main work and achievements in the article are summarized as following:Firstly, based on engineering practice, axial compression experiments and eccentric compression experiments of large sized round-ended CFST are carried out to study compressive mechanical behavior of round-ended CFST. Results show that:round-ended CFST under vertical load with good carrying capacity, but because corner stress concentration, bearing capacity improvement by stirrups effect is limited. Circumferential force distribution within the tube is uneven, which has great relation with tube shape. Because stirrups effect of steel tube on core concrete is small, component damage overall demonstrates the obvious fragility characteristic performance. Eccentric compressive experiment shows that eccentricity is major factor to affect bearing capacity. With increasement of eccentricity, bearing capacity will decrease. For large eccentricity conditions, load-lateral displacement curve of elastic stage is short and bearing capacity reduces much. Under ultimate load, steel tubular welded joint dehiscence at circular arc and tangential interface point, steel tublar compression zone have reached yield, while the other side is still in elastic stage.Secondly, based on experiments, round-ended CFST compressive mechanical properties are studied by finite element simulation. Finite element simulation shows that friction coefficient has little effect on round-end CFST bearing capacity. Core concrete strength has significant influence on component elastic-plastic properties. In the case of the same steel ratio, for round-ended CFST under axial compression, the greater of steel strength, the greater of bearing capacity, the stronger of component ductility. For round-ended CFST under eccentric compression, as the slenderness ratio increases, bearing capacity reduce, elastic stage shortens, but elastic-plastic stage extend. As concrete strength increase, the relative buckling coefficient gradually becomes smaller. As steel strength increase, bearing capacity increase, but rising slope slower gradually. As tube thickness increase, bearing capacity increase.Thirdly, based on unified theory, combined with experiment and finite element simulation analysis, bearing capacity formula of round-ended CFST under axial compression and eccentric compression are summarized, and the formula results compared with experiment data and finite element simulation results show results are in good agreement.Fourthly, based on reliability theory and reliability analysis module of ANSYS, round-ended CFST tower reliability of Houhu Bridge is systematically studied by Monte Carlo method and response surface method. Study shows that:for the control indicators of stress as the output reliability calculation, tensile strength to meet the requirements of structural reliability is98.69%, compressive strength to meet the requirements of structural reliability is98.89%. Analysis shows that the integration of finite element theory and reliability theory can be applied to complex structural reliability analysis.For round-ended CFST, the article gives a large number of first publication research results, which reveal round-ended CFST compressive mechanical properties, and systematic analysis round-ended CFST tower reliability. The research provides theoretical foundation of round-ended CFST further study and engineering application.