| Based on the "Performance and Analysis Research on Steel Box-Concrete Arch Structure" of the National Natural Science Foundation of China (51078373), the conception of prefabricated steel box-prestressed concrete continuous rigid frame bridge is proposed, which can overcome the distresses of cracking and excessive deflection in the main girder of prestressed concrete continuous rigid frame bridge. Aimed at the structural performance and design principle of prefabricated steel box-prestressed concrete(SB-PC) composite beam, the exploratory test and theoretical research are carried on. The main research contents and conclusions are as follows:①The idea that the steel box-concrete composite sections shall be selected according to the different stress condition along the main girder is put forward, the overall configuration optimized, the connector detailing studied and the construction procedure preliminarily explored. The analysis shows that the SB-PC composite continuous rigid frame bridge can overcome the distresses of cracking and excessive deflection in the main girder of prestressed concrete continuous rigid frame bridge and significantly reduce the bridge deadweight, promising a feasible way for the continuous rigid frame bridge to expected longer spans.②According to the structural and technical characteristics of the SB-PC composite continuous rigid frame bridge, the S-PC shear connection linking the bridge deck with the steel box girder is realized with post-cast concrete to fixate the shear connectors in prefab holes. Through the push-out tests of five S-PC shear connectors of two types combined with finite element analysis, the mechanical behavior of the connectors’full loading process is understanded, the force-transferring mechanism and the stress distribution law in different parts and directions are revealed. Based on statistical analysis of the test data, the load-slip constitutive equation of the S-PC shear connectors is established.③The influence of shear connectors’sectional area and height to the structural behavior of S-PC shear connectors is studied. The rule about the proportions of shear force shared by the upper and the lower shear connectors vary with the total shear force is also investigated. The S-PC shear connectors mainly present three failure modes: crush of the local concrete face in compression by the shear connector, shear failure of the welding seam at the root of the shear connector and excessive bending deformation of the shear connector. According to that, the bearing capacity formula avoiding the failure of S-PC shear connectors is proposed in this paper.④Fabrication process and mechanical behavior research of two SB-PC composite test beams are conducted, in which multiple static cyclic loading tests of each test beam are carried on under different upper loading limit. The results show that the critical load corresponding to the cracking of the SB-PC composite test beam’s concrete top slab increases with the effective concrete prestress. During static cyclic loading within the0.5Pu range, the test beam presents elastic behavior. Due to prestressing effect, the cracks in the concrete top slab of SB-PC composite test beam can close after unloading, but open again to be visible while it’s reloaded to0.33PV The crack width and number in the concrete top slab increase with the load. New cracks can hardly be seen after the load is over0.8Pu, but the existing cracks’length and width continuously grow with the load. When the load is close to the failure point, the read strain of the steel box’s top flange plate and bottom plate is higher than steel yield strain. The test beam finally failures as the steel box bottom plate is compressed to convex bucking and the bottom plate concrete is crushed showing obvious plastic failure characteristics.⑤Based on the existing research results of steel-concrete composite structure, and combined with the structural characteristics and test results of the SB-PC composite beam, the calculation formula for pre-cracking stiffness is proposed with the slippage effect of the top flange and bottom concrete slabs considered. The cracking moment calculation formula for the SB-PC composite beam is established through substituting the pre-cracking sectional resistance moment into the existing cracking moment calculation formula for the prestressed concrete beam, also with the slippage effect of the top flange and bottom concrete slabs considered. The post-cracking rigidity calculation formula for the SB-PC composite beam is established through simplification of the degrading law of the beam section rigidity as an analytical geometry curve, in which the two extreme cases of full-section work and work without the top flange concrete slab are made the boundary of the curve.⑥As an application example, the maximum negative moment beam segment (pear-top segment) of an SB-PC composite continuous rigid frame bridge with a main span of148m is tentatively designed, in which the calculation formulae proposed in the paper are used to determine the S-PC shear connector’s design, the cracking moment and the ultimate flexural bearing capacity of the main girder. |
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