| Hybrid girder can make full use of the advantages of steel girder and concrete girder, respectively. It has been widely used in bridge construction. But, because of the discontinuous of stiffness, the steel-concrete joint section is a structural weak Ness. Orthotropic steel decks(OSD) of steel girder are subjected to fatigue crack and pavement crack. For those reasons, the steel-UHPC lightweight composite deck(LWCD) system with plate rib, which is proposed by Prof. SHAO Xudong, is used in the bridge deck. And the UHPC layer is continuously extended to cover the steel-concrete joint section and a part of the concrete box girder(2.5m), to form ultra-high performance hybrid girder. LWCD can solve the two technical problems of fatigue crack and the disease of pavement layer of OSD. In this paper, a preliminary investigation is made on the steel-concrete joint section of ultra-high performance hybrid girder. The following work is done by the finite element analysis method:Firstly, by using ANSYS software, two finite-element models of steel-concrete joint section with or without UHPC layer were built and analyzed. Comparative analysis was done on the effect of UHPC layer on the mechanical performance of steel-concrete joint section under a single bending moment, axial force or bending and axial forces. The results show that the UHPC layer is used as a structural layer. It mainly affects the stress of steel roof and concrete in the upper part of the steel-concrete joint section, closer to the roof, the greater impact. And it has little effect on the stress of the steel base plate and concrete in the lower part of the steel-concrete joint section.Secondly, multi-scale finite element modeling method is described in detail to model the steel-concrete joint section of hybrid continuous girder bridge.Thirdly, based on multiscale finite element model, comparative analysis was done on the effect of UHPC layer on the mechanical performance of steel-concrete joint section. Similar to the traditional cantilever loading model, the results show that the UHPC layer is used as a structural layer. It mainly affects the stress of steel roof and concrete in the upper part of the steel-concrete joint section, and can significantly reduce the longitudinal stress of joint section 1 caused by wheel load.Fourthly, based on multiscale finite element model, the whole process of bridge construction is simulated. The results show that the stress of concrete steel-concrete joint section is mainly caused by the prestressing tendon. And in each stage, the prestressed tendon makes the concrete in a prepressing state. Before the bridge closure, the most unfavorable stage of steel-concrete joint section is in the stage of lifting steel box girder. After closure, the bridge structure transform from a cantilever system to a whole structure system, which improves the mechanical performance of the bridge structure, and slightly increase the overall compressive stress increased of steel-concrete joint section. After the bridge is completed, the steel-concrete composite section is in the vicinity of the anti-bending position, and the influence of the vehicle load on the stress distribution is not obvious.Fifthly, based on the multiscale finite element model, the stress level of each member in the steel-concrete joint section under the condition of the maximum negative moment is analyzed, and the stress transfer of each component is discussed. The results show that the stress of the steel-concrete joint section is not high, except for the stress concentration in the anchorage zone of prestressed tendon. And the concrete in the upper flange is in the prepressing state. The stress on the steel girder can be passed to the concrete girder through the steel-concrete joint section. However, it is necessary to pay attention to the phenomenon of the stress change of concrete and UHPC layer in the two ends of the steel-concrete joint section, due to the effect of the internal shear connector group. |
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