Key Techniques Study On Design And Construction For Large Size Coupled Round-ended Steel Tube-Filled Concrete Cable Stayed Bridge

Because of its structural of symmetry and can make full use of the steel concrete "hoop effect", round-shape Steel Tube-Filled Concrete (CFST) was the most widely used. The study on round-shape CFST is mainly applied in cable-stayed bridge, but for the round-ended CFST coupled column tower, the study of its mechanical properties is less, no less than the theoretical system.A large size round-ended Steel Tube-Filled Concrete coupled tower column was used in Houhu bridge with single tower and single cable plane in Wuhan. Its core concrete was C50 self-compacting micro expansion concrete with high dropping construction technology, the strength and the elastic modulus of concrete was 50 MPa above and 38GPa above separately. The suitable type, mixture ratio design, mechanical properties and high dropping construction technology of CFST, as well as the key technology in bridge construction system were studied systematically with numerical simulation, stress monitor and test study in this paper. The research achievement supplied the theory and technology for the design, preparation and application of micro expansion high-strength CFST materials.The originality innovation of this thesis is summarized as following:Firstly, the models of CFST tower with different cross-section (round-ended coupled limb, round-shape coupled limb, round-ended single limb, rectangular) were established, by imposing eccentric compression, the most unfavorable stress mechanical behaviors are compared. By analyzing stress cloud and extracting the stress data of the characteristic section, the results reflected the advantages of the mechanical behaviors of the round-ended CFST with coupled limb, which was applied in Houhu Bridge.Secondly, the mixture ratio design and high dropping construction test of CFST were conducted, the results show that: the C50 self-compacting CFST have reasonable mixture ratio and completely satisfied the requirements for high dropping construction technology, and its elastic modulus is for over 38.5 GPa, while the compressive strength is for over 60Mpa. After the completion of the tower in the construction of CFST tubular, the density detection results show that: the consistency of concrete in the steel of main tower is good, concrete and steel is seamless, which can reach the requirements for engineering design.Thirdly, the layout schemes of sensor, the measuring instrument and the load cases in the construction of Houhu Bridge's tower were introduced. According to the characteristic of construction in the cable-stayed bridge, the load cases are divided into axial compression case and eccentric compression case so as to analyze the mechanical behaviors of the rounded-end CFST.Fourthly, the stress-strain relationship of the round-ended concrete filled steel tubes were considered with test study and numerical simulation, and based on an example of project, considering the geometrical physical nonlinearities simultane-ously, to simulate the micro-expansive effect by making use of the variation of Poisson's ratio, the mechanical properties of the round-ended CFST coupled column were analyzed with the stress monitoring and numerical simulation in axial compression and eccentric compression, the interaction between the steel and the core, the stress condition of node in the area of the variable cross-section were analyzed with the contact analysis and the sub-model technology, and the most disadvantaged stress state of the structure under the triaxial compression are studied. The result shows that:With the variable concrete Poisson's ratio, comparatively, the bearing capacity analysis considering the variable concrete Poisson's ratio enables to enhance the design capacity, the stress of the structure changes little in axial compression, but increases large while bearing eccentric loads, especially it can make full use of the characteristics of the form of this structure, contact analysis and sub-model method were used to analyze the round-ended CFST coupled tower column and the variable cross-section area respectively, the results reflected the change rules of stress of round-ended CFST tubular tower in axial compression case and eccentric compression case, in addition, the most disadvantaged stress state of the structure under the triaxial compression was found out, the results also prove that the theoretical data is consistent with the measured data, which can indicate that the selection of unit, material and various parameters are reasonable, can fully reflect the carrying capability in the construction of tower, provide the reference for the construction and monitoring for bridge.Lastly, the study on the dynamic characteristics of round-ended CFST Bridge was analyzed and the results showed that: the dynamic characteristic of bridge is normal in constructed of bridge and the structure is stable.In the analysis of the mechanical behaviors of round-ended CFST tower applied in Houhu cable-stayed bridge with single tower and unsymmetrical single cable plane in Wuhan, which was a innovative structure. An excellent and reasonable design of bridge was obtained with the selection of different tower with different cross-section, the mixture ratio design, stress monitoring and the numerical simulation, the results reflected the change rule of stress of circle-end CFST tower under axial compression case and eccentric compression case. In addition, the most disadvantaged stress state of the structure was found out. Some measures are proposed to this kind of structure members basing on the results of the measured data and the theoretical analysis.