| Concrete-filled steel box beam is composed of steel box and concrete partially filled in steel box. It has excellent properties such as high capacity, high rigidity , high ductility and convenient construction as traditional composite beam of steel and concrete. The enhancement in structural properties is due to the composite action between the steel plates of box and the concrete. The inward buckling of the steel plates of the box is prevented by the concrete, thus increasing the local buckling strength of the structure, and more sefficient use of the strength of steel. Conversely, the confinement created by the steel plates of box enhances the material properties of concrete by putting the concrete under a triaxial stress state. A research project 'Research on the local buckling of concrete-filled steel box beam' has been undertaken by Civil school of Hunan University of Science and Technology, which is sponsored by the National Natural Science Fund of China. A research project 'Research on new type composite beam' has been undertaken, which is sponsored by the Natural Science Fund of Hunan Province. A research project 'Research on the structural behavior of continous concrete-filled steel beam' has been undertaken, which is sponsored by the Science Fund of Hunan Province office of education. The main contents of these projects include: (1)experimental research of the structural behavior on concrete-filled steel box beam, (2)calculating model of local buckling on top plate of concrete-filled steel box beam, (3) local buckling strength of the web of concrete-filled steel box beam, (4)the incorporating buckling of the top plate and webs of concrete-filled steel box, the correlativity of the strength and local buckling of the composite beam, (5)the structural behavior of continous concrete-filled steel beam.As part of these research projects, the main content of the dissertation is as follows.(1) The experimental research of the structural behavior of simply-supported concrete-filled steel box beam is conducted. Tests are carried out on 6 specimens including 4 concrete-filled steel box beams and 2 steel box beams under static loads and the phenomena observed during the tests of specimens are described in detail, and the deflection of beams and the data of strain of steel box during tests are recorded. The results indicate that the buckling model and postbuckling behavior of plates of the steel box are changed, and the local buckling strength of plates of the steel box are enhanced, and higher capacity and ductility of the beam are provided with after filling concrete in the steel box. The ratio of the width and thickness of the box's top plate and webs influences the structural behavior of the beam.(2)The local buckling of concrete-filled steel box beam is analyzed. The buckling strength calculating formula of rectangular plate on rigid base is founded, of which the unloaded edges are rotationally constrained elastically and the loaded edges are subject to in-plane axial action. The elastic constrained rigidity of the calculating plate is ascertained by considering restricting action of core concrete and adjacent plates. Then the formula is used to calculate the local buckling strength of top plate and webs of concrete-filled steel box beam and to ascertain the limited value of the ratio of width and thickness of steel box's composing plates in design.(3)The elastic and plastic behavior of concrete-filled steel box beam is studied. After the elastic analysis of concrete-filled steel box beam, the calculation of its rigidity and ultimate elastic strength is putted forward. Then after full-range analysis of concrete-filled steel box beam on combined methods, the ultimate flexural strength is presented. 3-D non-linear finite element analysis of concrete-filled steel box beam has been carried out by Ansys soft.(4) The experimental research of the structural behavior of continous concrete-filled steel box beam is conducted. Full-range tests are finished on 3 specimens including 2 two-span continous concrete-filled steel box beams and 1 steel box beams under two concentrated loads. The results indicate that the local buckling strength of the steel box around the mid-bearing is enhanced, and the structural behavior of the continous beam around mid-bearing is improved, where negative bending moment is suffered, and higher capacity and ductility of the continous beam are provided with after filling concrete in the steel box.(5) Elementary explore of design and application of concrete-filled steel box structure is presented. Firstly the main design parameters of concrete-filled steel box are presented. Secondly the elementary assumption of its application in continous beam bridge and cable stayed bridge is proposed.
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