| Considering the main weaknesses of the concrete arch bridge, such as the high and long-term risk during construction, this dissertation proposes the concept of "Vertical Rotation Steel-Concrete Composite Bridge", which is supported by both "Performance and Analysis Research on Steel Box-Concrete Arch Structure" of the National Natural Science Foundation of China (51078373) and "Design and Key Construction Technologies of Vertical transfer on Steel-Concrete Composite Bridge" of the Western Transportation Construction Science and Technology Projects (200631881448). Experimental study and theoretical analysis are applied on the detailed construction, structural performance and computational methods of the steel box-concrete composite arch concrete systematically. Main contents and conclusions are as follows:1. The advantages of conventional concrete arch bridge, as well as the limitations, are analyzed. According to the load-bearing of different segments in the non-hinged arch bridge, the composite sections of steel box-concrete composite arch bridge corresponding to these segments for varying load-bearing performance are proposed, which improve the detailed constructions of the main arch structure. The analysis shows that, maintaining the main advantages of conventional concrete arch bridge, the steel box-concrete composite arch bridge not only significantly reduces the risk of bridge construction, but also increases the capacity of seismic, shock resistance and ductility during the service period.2. For the compressive and bending member under the positive moment as well as the axial force, the composite sectional construction is proposed when the concrete is poured on the top slab of steel box girder, which can resist both the eccentric pressure in the section and the tensile pressure by the unfavorable load combination in the lower edge of the section. A steel frame is formed by the longitudinal reinforcements and the stirrups crossing through through the holes in the top slab of steel box girder, which promotes the concrete and the steel box to generate an integral PBH shear connector construction. This will make the connection between the steel box and concrete more reliable, without special shear connector structural materials or more constructional processes.3. Experimental researches on the shearing capacity of several sets of PBH shear connector constructions and a set of traditional PBL shear connector constructions are carried out. The results show that the shear stiffness and load-bearing capacity of the PBH are better than that of the PBL. It is found that there are three main failure modes of PBH. The discriminant formula for the constructional requirements is proposed to avoid the buckling failure or welding failure of the opening stiffening rib slab. Combining with the sophisticated finite element analysis, the load-slip constitutive model for the PBH shear connector construction is established. And through the parameter analysis, the semi-theoretical and semi-empirical formula of the PBH connector's shear strength is proposed.4. Experimental researches on the load-bearing capacity of the steel-box and concrete composite compressive and bending members are carried out. The over-all researches on the load-bearing process, failure patterns and load-bearing capacity of the steel-box and concrete composite members subjected to simple bending, eccentric compression and axial compression. Based on the experimental results, the entire process of load-bearing in bending members and large eccentric compressive members can be divided to three stages:the elastic stage, the elasto-plastic stage and the collapse stage.5. For the construction and failure characteristics of steel box-concrete composite compressive and bending members, the failure characteristics and discriminant method of large eccentric compressive failure(plastic failure) and small eccentric compressive failure(brittle failure) are proposed. And the discriminant formulas to distinguish the two failure patterns are deduced theoretically.6. For the constrained characteristics of concrete in the steel box-concrete composite members, according to the different constraint effects in the roof and ribbed stiffener of steel box and the concrete inside and outside of the reinforced frame, they are divided into three parts as follows:strong constrained area, weak constrained area and unconstrained area, and the constrained characteristics of concrete in each area are analyzed. Based on the direct homogeneous theory of non-homogeneous materials, a single-medium homogeneous constitutive model for the constrained concrete in the steel box-concrete composite members is established, and the parameters of the model are defined combining with the measured data derived from the compressive and bending experiments.7. As the steel box and compressive concrete have the same curvature and submit to the assumption of plane section, the relationships between the slip, load and shearing stiffness of the interface in the steel box-concrete composite arch members are deduced. Based on the curve of load-slip, the fiber model is applied to establish the whole process analysis of steel box-concrete composite compressive and bending members considering interface slip, and the corresponding analysis process (SCCA) is built up by applying Matlab. Comparing with the American special composite section analysis software X TRACT, the computing results of the two methods are in agreement on the whole, and the SCCA can reflect the load-bearing characteristics of the whole process in the steel box-concrete composite section more accurately. Also the ultimate load-bearing capacity obtained by SCCA program is more identical with the experimental results.8. The SCCA program is applied to analyze the relation between the stiffness of shear connector construction and the load-bearing capacity of steel box-concrete composite members. It is found that if the shear load is less than half of the PBH shear resistance of shear connector construction, when calculating the load-bearing capacity of steel box-concrete composite members, the effect of the interface slip between the top slab of the steel box and the concrete above can be neglected. Otherwise, the load-bearing capacity can be calculated by the SCCA program.9. Combining with the experimental data and theoretical analysis, the load-bearing capacity calculation formulas for simple bending, axial compressive and axial tensile steel box-concrete composite members are derived, and the M-N relation curves are reduced to triple-fold relation by the load-bearing capacity points of simple bending, axial compressive and axial tensile. Based on these, the simplified M-N load-bearing capacity calculating method for steel box-concrete composite compressive and bending members is established. |
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