Research On Flexural Mechanical Properties Of Group-nail Steel-concrete Composite Box Beams

Group nail steel-concrete composite box beam is a composite component that combines the steel box beam and the concrete bridge deck through the Shear connector.It is a structure that can give full play to the mechanical properties of concrete and steel,and can use the material reasonably effectively.Although the domestic and foreign researchs on steel-concrete composite structures is relatively extensive,previous research on the bearing capacity of group nail steel-concrete composite structure are few,and there are many research on the horizontal shear force of nail,there are few researches on carrying capacity and vertical pull-out performance and the elastoplastic development process and failure mode of group nail steel-concrete composite beams are not clear,so further research is needed in this aspect.In this paper,the static load test and numerical analysis of the group nail steel-concrete composite beams are used to obtain the concrete slab strain curve,steel box beam strain curve,relative horizontal slip curve and load-deflection curve.By analyzing the above curve: elastoplastic development process,failure mode,nail shear resistance,pull resistance and load carrying capacity,conclusion are followed:(1)Through experimental research and numerical simulation analysis,the group nail concrete composite beam can be roughly divided into three stages in the process of stress: elastic stage,elastoplastic stage and plastic stage.In the elastic phase,the overall performance of the composite beam is good,the stress-strain curve is linear,and the deflection increases linearly with the load.After loading to the crack of the concrete wing plate,the strain rate of the steel box beam is accelerated,and the load-deflection curve begins to become nonlinear,the composite beam enters the elastoplastic stage,the stiffness decreases.Then the deflection deformation of the composite beam span increases significantly,the stud is subjected to large vertical tension,the stud is damaged by tension,and the concrete and steel around the stud The vertical separation of the box girder and the hollowing phenomenon lead to the crushing of the concrete and the destruction of the specimen.This stage can be considered as the plastic development stage of the composite beam.(2)The failure mode of group-stud steel-concrete composite beams is: during the step-by-step loading process,the studs are subjected to large vertical pull-out forces,and the concrete around the studs is also subjected to upward pulling forces.As the load level increases,the studs are damaged by tension.Due to the interlocking of the studs and the concrete,the concrete and the steel box beams around the studs are separated,and the hollowing phenomenon occurs,causing the concrete to be crushed and the test piece declared to be damaged.(3)By analyzing the load-slip curves,it is concluded that there is no obvious horizontal slip during the entire loading process of the static load test,This,indicates that the stud-connected composite beam has excellent resistance to horizontal shear and can provide the composite beam with sufficient shear resistance.However,horizontal stratified cracking occurred between the steel box girder and the concrete,and it was initially judged that the studs had suffered pull-out failure,indicating that the stud connectors needed to be improved in terms of pull-out resistance.(4)Through the analysis of the bearing capacity of the group-nail steel-concrete composite beam,the test shows that the ultimate failure bearing capacity of the groupnail steel-concrete composite beam is 149 t,and no damage occurs when the finite element numerical model reaches the limit load of 149 t.The poor anti-pulling performance of the studs leads to a reduction in the bearing capacity of the composite beam.