Research On The Configuration Of Steering Block Of External Prestressed Tendon In Box-girder Bridge Composed Of One-way Prestressed UHPC

Normal concrete prestressed box girder bridge has characters of definite load conditions,excellent torsional performance,convenient erection and installation,and excellent visual effect under the bridge.It is a kind of bridge type widely used in practical engineering.On the one hand,normal concrete has low tensile strength,and the concrete box girder web is easy to crack during operation;on the other hand,the ordinary concrete shrinkage and creep effect is complicated,and the prestress loss under alternating load is difficult to estimate,ordinary concrete pre The long-term undercut problem of the main girder of the stress box girder bridge in engineering practice is outstanding.The downward deflection of the main beam will aggravate the development of the crack of the beam,which will lead to the decrease of the stiffness of the beam,which will further aggravate the development of the deflection.The coupling effect of these aspects has become the bottleneck of the development of this type of bridge.With the development of ultra-high performance concrete(UHPC)materials,Professor Shao Xudong of Hunan University proposed the concept of a new type of prestressed UHPC box girder bridge.This bridge system combines the excellent mechanical properties of UHPC in strength and creep.It is expected to fundamentally solve the two major diseases of cracking and lowering of ordinary concrete box girder bridges.Through the relevant experimental research,the research team has mastered many structural properties of the UHPC box girder bridge,and the problem of the arrangement and steering of the external prestressed beam in the UHPC box girder remains to be further studied.Due to the low tensile strength of ordinary concrete,no matter the traditional block,rib and diaphragm type steering block structure can not balance the light weight and high bearing capacity,the steering block based on UHPC material design The form of the traditional steering block cannot be directly quoted.In addition,the rational design of the UHPC steering block is related to the structural characteristics of the UHPC box girder,the prestressed beam arrangement,etc,and needs to be considered in the specific parent structure.Through the relevant experimental research,the research team has mastered many structural properties of the UHPC box girder bridge,and the problem of the arrangement and steering of the external prestressed beam in the UHPC box girderremains to be further studied.Contrary to the low tensile strength of ordinary concrete,the traditional block,ribbed and transverse baffle steering structures are bulky and complex.In this paper,in order to combine the excellent mechanical properties of UHPC and the layout characteristics of dense partitions of UHPC box girder,a lightweight,high-capacity UHPC steering structure suitable for external prestressed beam steering is proposed and discussed in the following aspects:(1)According to the UHPC box beam dense partition configuration and its cantilever assembling construction method,analyze the arrangement and steering of the external beam at different construction stages,thereby clarifying the three basic turning positions of the steering block in the UHPC box girder.And the different beam girder plates that may be affected by the in vitro beam steering at these three locations.(2)Combining the force mechanism of the ribbed steering block in the traditional ordinary concrete steering block and the configuration of the dense diaphragm in the UHPC box girder,a new UHPC rib block steering structure is proposed.The steering structure is partially thickened to form a steering body in the UHPC box girder transverse partition,so that the box girder plate such as the transverse baffle and the web can be integrated with the steering block to bear the external beam steering force.(3)Taking a proposed UHPC box girder bridge in Guangdong as the engineering background,the prestressed system was designed and tested,and the whole bridge was calculated by Midas software.The calculation results met the design requirements.According to the steering position of the external prestressed beam of the bridge,the linear elastic local model is established by ANSYS software to analyze the different stress fields caused by the external beam steering force at each steering position,and the most unfavorable web bucking steering block is The analysis was carried out separately,and five local effects under the external beam steering force were summarized.(4)By designing the full-size test piece of UHPC rib block steering block,the reaction of the web,the diaphragm and the self of the UHPC rib block steering block under the vertical steering component is investigated.The observation and summary are carried out.The development of the steering block itself,the diaphragm and the web strain are monitored and analyzed.The crack safety factor of the UHPC rib block steering block can be 3.7.(5)The nonlinear finite element software ABAQUS was used to simulate the test process,and the load-deflection curve and crack distribution in the finite elementcalculation results and test results were compared to verify the reliability of the finite element modeling method.The parameters such as UHPC axial tensile strength,lead angle and steering block reinforcement are analyzed.The recommended reinforcement diagram of UHPC rib block steering block is given.