Study On Mechanical Properties Of 600MPa Steel Bar Reinforced Concrete Column Subjected To Axial Compression Under Repeated Loading

600MPa steel bar is a new type structural steel bar,which has been investigated and developed recently after 400MPa and 500MPa series of high strength steel bars.The universal application of 600MPa steel bar is not only accord with the idea "four saving one environment protected" requests but also meets the development needs of construction industry of our country.The mechanical properties of reinforced concrete axial columns with 600MPa grade longitudinal bars were studied,which provides some theoretical basis and experimental basis for the application of 600MPa steel bar.Ten axial specimens with 600MPa steel bar,one with 400MPa steel bar and another one with 500MPa steel bar has were tested under monotonous and repeated load.The effects of loading method,concrete strength,reinforcement ratio and stirrup ratio on failure characteristics,peak strain of concrete,stress deformation of reinforcement and load-displacement curves of 600MPa steel bar concrete axial compression columns were studied.The results show that the failure mode of concrete columns with 600MPa steel bar under axial load are similar to that of normal reinforced concrete columns.The stress-strain curve of 600MPa grade reinforced concrete column under repeated axial load is basically the same as that under monotonic load,but the curve is slightly different in the later stage.The bearing capacity of axial compression members can be calculated according to the formula specified in the code for design of concrete structures(GB 50010-2010).The design value of the compressive strength of the 600MPa steel bar in axial compression members can be taken as the value of 420MPa.The unloading curve under repeated loading was fitted and the relationship equation between unloading strain and residual strain was established.And reloading curve under repeated load was fitted and the relation equation between residual strain and reloading strain was established.The numerical simulation of the 600MPa steel bar concrete axial compression column was carried out by using ABAQUS finite element model.The results of finite element analysis were basically consistent with the experimental results.Based on simulate and experimental results,the difference of 600MPa steel bar concrete axial compression column specimens under monotonic and repetitive loads were explored.