Study On Mechanical Behavior Of Steel Beam-precast Floor UHPC Jointed Joints

Ultra-high Performance Concrete(UHPC)is a new type of concrete material,which has several times higher compressive,tensile and ductile deformation capacities than normal concrete.It changes the problems of low strength and easy cracking of normal concrete under tensile or shear load.The application of UHPC can effectively shorten the length of reinforcement overlap and anchorage in the post-pouring area of the fabricated concrete structures,reduce the size of post-pouring area and the workload of field wet operation,which shows that UHPC has significant performance and economic advantages.However,the application of UHPC has changed the mechanical mechanism and failure mode of traditional fabricated composite beams.Therefore,UHPC assembled steel-concrete composite beams with different connection structures was tested under push-out tests.The failure mechanism and failure mode of UHPC assembled steel-concrete composite beams were revealed by experimental results and theoretical analysis.The corresponding calculation method of shear capacity was established.The main research work and achievements are as follows:(1)Fifteen rectangular UHPC post-pouring prefabricated steel-concrete composite beams were designed.The effects of transverse reinforcement ratio at the top of concrete precast slabs,concrete-UHPC interface area and the extension length of steel bars at the bottom of concrete precast slabs on the shear capacity of specimens were studied.The results show that the longitudinal shear capacity of the specimen can be improved by increasing the diameter of the reinforcement,shortening the spacing of the reinforcement,increasing the interface area and extending the bottom reinforcement.(2)Eight groove-shaped UHPC post-cast belt assembled steel-concrete composite beams were designed.The effects of the size of UHPC shear keys and the placement of shear reinforcement on the shear capacity of specimens were studied.The results show that reasonably increasing the size of UHPC shear bond can greatly improve the interfacial shear capacity with good economic benefits,increasing rear shear reinforcement can further improve the shear capacity.(3)The effects of different structural measures on the failure mode,crack mode,load-slip characteristics and ultimate bearing capacity of composite beams were analyzed.It was proposed that the shear bearing capacity of the interface is mainly composed of the bond force generated by concrete,the interfacial friction caused by the steel bar,and the pinning effect of the steel bar itself.Combined with the actual structural form and specimen failure phenomenon,it is considered that the bearing capacity of some structural types of specimens contains the shear effect provided by UHPC shear key.The calculation formula for the shear strength of the interface between ordinary concrete precast slab and UHPC was established,and a new design method for UHPC wet connection joint of assembled monolithic steel-concrete composite beam with application prospect was proposed.