The Research On Shear Behavior Of Reinforced Ultra High Performance Concrete Short Beam

Recently, reinforced concrete deep flexural members are increasingly used incivil engineering because of their tremendous bearing capacity. Deep flexuralmembers are inclined to shear failure in earthquake or under large concentrated loadsince they usually bear fairly high shear force but a small moment. In order toenhance shear resistance, deep flexural members usually magnify depth and locatelots of steel bars inside, which result in more material consumption and difficulties inconstruction. For its excellent mechanical properties, Ultra High PerformanceConcrete (hereafter referred to UHPC) has been developed rapidly in the last twodecades. UHPC exhibits excellent tensile strain-hardening properties which could beused in shear-based members or flexural members under high shear stress. Moreover,the transverse reinforcement could be reduced or even cancelled. The shearperformance of reinforced UHPC is discussed by experimental research andtheoretical analysis in this paper.Firstly, the material properties of UHPC are tested, including cubecompression tests, uniaxial tensile tests and uniaxial compression tests. The risingstages of compressive stress-strain curve and tensile stress-strain curve are obtained,which show large compressive strain and excellent tensile strain-hardening propertiesof UHPC. Based on the material properties tests, the shear tests of three short beamsare executed with the variable values of cementitious materials and ratios of shearspan to effective depth. Shear failure has occurred to three beams. The reinforcedconcrete short beam has undergone shear compression failure, but the reinforcedUHPC short beams have undergone flexure-shear failure. Based on the syntheticanalysis of the characteristic loads, the stress-strain relation of longitudinalreinforcement and stirrups, diagonal section strain of concrete and load-midspandeflection curves, the UHPC short beams show higher value of cracking load andultimate load and exhbit better ductility compared with the reinforced concrete shortbeam.By using finite element analysis software ABAQUS, numerical simulations ofthe reinforced UHPC short beams are conducted, the numerical results andexperimental results are compared. Meanwhile, expanding numerical analysis hasbeen carried out to discuss the ratios of longitudinal reinforcement and transverse reinforcement which have not been considered in experiments. Based on the finiteelement analysis, a softened strut-and-tie model is established. The model takes intoaccount the softening of concrete under biaxial stress, stirrup stress inhomogeneity inthe shear span. A formulation of shear resistance under concentrated load has beenproposed, and it could considerablely coincide with experimental results and be usedto predict shear resistance of UHPC short beams.