| Separation problems in CFST arch bridge are common and complex engineering problems. This dissertation developed a series of theoretical analysis and case study to the separation effects to mechanical behavior on CFST arch bridge, proposed complete debonding calculation model for CFST arch bridge, aiming at separation phenomenon between steel tube and filled-concrete, researched the reason of separation, separation influence degree on mechanical behavior of CFST arch bridge, on this basis proposed the economical and effective treatment measure for separation.The following are main research contents and achievements:(1) Based on plane strain theory, This dissertation derived the calculation formulations for calculating the tensile stress and the shear stress on the interface between the steel tube and filled-concrete of CFST component, under the axial pressure, temperature load and shrinkage strain of filled-concrete. Taking common materials and section size CFST components as case studies, the calculated results indicate that separation shall occur mainly by occasion of interface tensile stress over bond strength under temperature load and shrinkage strain of filled-concrete. If no measure was taken, appearance of partial separation is inevitable.(2) This dissertation proposed complete debonding calculation model of CFST arch bridge, the actual mechanical behavior of CFST arch bridge should be between complete debonding and complete bonding. Based on the complete debonding assumption, this dissertation proposed adopting finite element method to calculate the radial distribution load between steel tube and filled-concrete, and provided calculation examples.(3) Based on the calculation model of complete debonding on the interface between steel tube and filled-concrete, this dissertation derived the calculation formulations for calculation internal force distribution of steel tube and filled-concrete, by using the method of structural mechanics. For constant-section single tube CFST rib, section total internal force on the situation of complete debonding is equal that of on the situation of complete bonding, moment ratio of steel tube and filled-concrete on the situation of complete debonding is equal to bending stiffness ratio of them. For trussed CFST rib, section total internal force on the situation of complete debonding isn't always equal that of on the situation of complete bonding, moment ratio and axial force ration of steel tube and filled-concrete on the situation of complete debonding aren't equal to bending stiffness ratio and tension and compression stiffness of them .(4) Based on the calculation model of complete debonding on the interface between steel tube and filled-concrete, this dissertation theoretically researched the change of stiffness of CFST rib by using principle of virtual work. For constant-section single tube CFST rib, interface complete debonding basically will not lead to reduction of structure stiffness. For trussed CFST rib, interface complete debonding will lead to reduction of structure stiffness, the degree of reduction is related to rise-to-span ratio, height of truss, section of CFST rib and the types of loading.(5) Based on the calculation model of complete debonding on the interface between steel tube and filled-concrete, this dissertation derived the calculation formulations for calculating the creep self stress of steel tube and filled-concrete, proposed adopting finite element method to calculate creep secondary stress and internal force, and provided calculation examples. The results indicate that the difference of internal force of the steel tube and filled-concrete on the two situation of complete debonding and complete bonding after the accomplish of shrinkage and creep is smaller that of formation stage of the bridge, the internal force increment due to temperature load on the two situation of complete debonding and complete bonding is different, for constant-section single tube CFST rib, the vertical displacement due to temperature load on the two situation of complete debonding and complete bonding is basically equal, for trussed CFST rib, the vertical displacement on the mid-span due to temperature load on the situation of complete debonding is slightly larger that on the situation of complete bonding.(6) Based on the calculation model of complete debonding on the interface between steel tube and filled-concrete, on the basis of the BDCMS software programmed by professor YAN Dong-huang, this dissertation increased the function of calculating the ultimate bearing capacity in plane of CFST arch bridge, and verified the correctness of the program by outcome of model tests. Taking a constant-section single tube CFST rib and a trussed CFST rib as case study, this dissertation analyzed the complete debonding influence on ultimate bearing capacity in plane. The results indicate that for constant-section single tube CFST rib, ultimate bearing capacity decrease only under the full span uniform distribution load on the situation of complete debonding, decrease percentage is about 10%, but for trussed CFST rib, ultimate bearing capacity significantly decrease under various type load, decrease percentage is between 20% and 60%, the complete debonding influence on ultimate bearing capacity in plane for trussed CFST rib is larger that for constant-section single tube CFST rib.(7) This dissertation proposed separation countermeasure of setting inner flange structure to limit the slide between the steel tube and filled-concrete in some point and adding expansive agent into concrete to decrease height of separation, proposed the structure type of inner flange, design method of strength and stiffness of inner flange. Taking MaoCaoJie bridge and a constant-section single tube CFST arch bridge as case study, This dissertation analyzed the effects of inner flange structure on mechanical behavior, the results indicate that inner flange structure can significantly improve mechanical behavior of the CFST arch bridge on the situation of complete debonding, the mechanical behavior with the separation countermeasure is close to that of complete bonding.
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