| Steel girder is used in the main span of hybrid girder cable-stayed bridge to reduce the self-weight and increase the span;concrete girder is used in the side-span to anchor and improve the overall rigidity of the whole bridge.Therefore,the span of hybrid girder cable-stayed bridge is longer than that of ordinary cable-stayed bridge,and the ratio of side-span to mid-span is smaller than that of ordinary cable-stayed bridge,which has a very broad application prospect.As the connection part of the hybrid girder cable-stayed bridge,it is too complex to obtain the mechanical properties of the steel-concrete joint section accurately.At present,the research on steel-concrete joint section are not enough to explain the transmission mechanism and satisfy the requirement in engineering design.Based on an actual hybrid girder cable-stayed bridge constructed by horizontal rotation method as study case,the mechanical properties of steel-concrete joint section are studied in this paper..The specific research contents are as follows:(1)By establishing the finite element model of the whole bridge,the internal forces and stress of the steel-concrete joint section are calculated at the the rotation stage,the completion stage,the stage of a decade after completion and the operation stage.The results show that the prestress of the steel tendons anchored on rear bearing plate is the main source of the axial force applied on the joint section.The concrete creep causes a redistribution of the internal forces of the whole bridge,which especially influence the bending moment of the steel-concrete joint section.As a result,the bending moment at the stage of a decade after completion should be taken as the control parameter of the joint section.(2)The mechanical properties of the steel-concrete joint section under the most unfavorable load combination are studiesd at the operation stage,through the calculation and analysis of the solid element model of the steel-concrete joint section.The stress distribution of the top and bottom plates,webs,stiffeners,auxiliary T-stiffeners,diaphragms,rear bearing plates,mediastinum plates,filled concrete,concrete girder are analyzed.It is clealy seen that auxiliary T-rib of which the height is variable can effectively disperse the axial pressure of the top and bottom plates.The rear bearing plate mainly plays a role in the loads transmition and loads spread which come from the reinforcement steel box and prestressed tendons.(3)The vibration string sensors are used to measure the stress of the joint section at the rotation stage and the completion stage.It can be concluded that the joint section model of which steel and concrete components are rigidly connected can be used to predict the stress state of the reinforced steel box girder and the concrete girder accurately.The effect of cable and prestressed tendon will lead to a result that the longitudinal stress distribution of the joint section is not uniform,so the shear lag effect should be considered in design to provide enough safety reserve.The steel diaphragm and concrete beam can be arranged to improve the transverse rigidity of the joint section and reduce the transverse stress of the joint section.At the same time,the excessive arrangement of transverse prestressed tendons should be avoided,which leads to the up-warp deformation and additional internal force of the joint section.(4)The differential equation of multi-row shear connectors under concentrated load is proposed.The solid element model of bottom cells is established to analyze the shear distribution regulation.The results indicate that the shear force at either end of multi-row shear connectors in joint section with rear bearing plate is greater than that in the middle location.Meanwhile,the distribution of the shear force of the shear connectors is greatly influenced by the prestressed tendons and the holes on plate.When the standard formula is used to estimate the shear force of shear connectors,the results may be unsafe. |
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