Experimental Study On The Interface Shear Behavior Of Precast UHPC Composite Beam With Shear Pocket

Under the background of bridge engineering requiring light weight,high strength,rapid erection,durability,environmental protection and sustainable development,prefabricated structures are more and more used in bridge construction,with good quality,durability and life cycle cost reduction of full-depth prefabricated structures,which can accelerate the construction speed and reduce the impact on traffic during construction.Compared with traditional concrete prefabricated components,precast UHPC composite beams can overcome the defects of ordinary concrete,such as easy cracking,poor durability and large section,due to the excellent material properties of UHPC.Due to the lack of relevant UHPC design codes,the application of prefabricated UHPC composite beam in engineering has been greatly limited,and the interface of composite beam is often the weakest portion of the structure,so is the interface of UHPC composite structure.At present,the research on the interface shear performance of precast UHPC composite structure is very limited,and the calculation formula of the interface shear capacity summarized based on traditional concrete is too conservative for the estimation of the interface shear performance of UHPC composite beam,therefore the research on the interface shear performance of precast UHPC composite beam is very important scientific research and socio-economic benefits.In this paper,the interface shear behavior of a new shear pocket was investigated,which connected precast utra-high performance concrete(UHPC)beam and precast UHPC bridge deck,the U stirrups was extended from UHPC beam and inserted into shear pocket of bridge deck,and then the pocket was grouted with concrete.through 16 push-out specimens,the shear resistance of UHPC composite beams is studied,it can provide some suggestions and references for the formulation of relevant specifications and bridge design.The principal study and conclusions of this paper are as follows:(1)taking the reinforcement ratio(3.7%,2.8%and 2.0%),precast beam concrete type(UHPC,NC(ordinary concrete))and precast deck concrete type(UHPC,NC,LC(lightweight aggregate concrete))and slot filled concrete type(UHPC,NC)as research parameters,the failure mode,ultimate load,residual load and relative slip of the test piece are studied Based on the shear friction theory,the influence rule and mechanism of each parameter are analyzed.(2)Test results showed that the reinforcement ratio plays a significant role in ultimate load V_uand residual load V_r.Secondly,Secondly,the ultimate load V_u and residual load V_r are dominated together by the grouted concrete type and the concrete type of precast beam.Under the same reinforcement ratio,the ultimate load V_u of U-U interface is 1.51 times of N-U interface and 1.87 times of N-N interface.Thirdly,The precast bridge deck concrete type has little effect on the shear behavior.At the same time,it is found that the dowel action of reinforcement is mainly affected by the diameter and the concrete strength grade.(3)Finally,compared with the existing five codes,it is found that the existing codes are conservative in the estimation of the shear capacity of the pocket interface of prefabricated UHPC composite beams,and the relevant formulas are modified.