Experimental Study On Structural Behavior Of High-Strength Concrete Columns Confined By High-Strength Rebar

Using high-strength materials is an effective way to achieve energy conservation, emission reduction and sustainable development. The applications of high-strength rebar and high-strength concrete can significantly reduce the use of resources, which can generate considerable economic benefits. While using high-strength rebar to confine high-strength concrete, the peak stress and peak strain of concrete and bearing capacity of structures can be enhanced. Meanwhile, the ductility of structures can be improved. However, researches of structural behavior of high-strength concrete columns confined by high-strength rebar are still not sufficient nowadays. In this paper, the structural behavior of high-strength concrete columns confined by high-strength rebar is studied by experimental research. The main work and achievements are as follows:Axial compression experiments of 13 high-strength concrete(C60) columns reinforced with HTB650 longitudinal bars and HTH800H confinement stirrups were carried out. The failure mode, load-deforming curve, ductility, the peak stress of longitudinal bars, the peak stress and peak strain of confined concrete were experimentally studied. Based on the results, the influences of stirrups diameter, stirrups spacing, stirrups yield strength and volumetric ratio of stirrups on structural behavior of columns were analyzed as well. Then the equations for calculating the bearing capacity of high-strength concrete columns confined by high-strength rebar with axial load is proposed, which the design value of stirrups is 660 MPa and that of longitudinal bars is 540 MPa.The test results of axial compression experiments show that: Firstly, compared with those columns confined by normal-strength rebar,the columns confined by high-strength rebar exhibits better strength and ductility. Secondly, the improvement of peak stress and peak strain of confined concrete and ductility of specimens is positively correlated to confinement pressure. Thirdly, the confinement pressure is in positive correlation to volumetric ratio of stirrups. Fourthly, the confinement pressure provided by stirrups with thin and small spacing is better than that provided by stirrups with thick and large spacing. Lastly, longitudinal bars in the columns confined by high-strength rebar can yield at peak load.Four high-strength concrete(C60) short columns reinforced with HTB650 longitudinal bars and HTH800H confinement stirrups were tested under the low frequency cyclic loading with axial compression. Based on the test results, the influences of span-depth ratio, yield strength of longitudinal bars, stirrups strength, stirrups diameter and volumetric ratio of stirrups on failure mode, hysteretic behavior, ductility, ultimate displacement angles, deformation capacity and strain of longitudinal bars and stirrups were analyzed.By analyzing experimental phenomena and results of the four high-strength concrete short columns, it can be concluded that: Firstly, compared with short columns reinforced with ordinary-strength rebar, columns reinforced with high-strength stirrups have higher safety margin. Secondly, better restraint is provided by high-strength rebar after the peak load, which can improve ductility and anti-collapse capacity of columns. Thirdly, the poor ductility caused by span-depth ratio and brittleness of high-strength concrete could be solved by high-strength rebar. It could exhibit well displacement ductility even if the volumetric ratio of stirrups is less than 1.2%. Fourthly, it is more reasonable to use ultimate displacement angles to reflect the ductility of high-strength concrete columns confined by high-strength rebar. In the end, the yield strength of high-strength stirrups should be reduced when calculating stirrups characteristic value.