Study On Mechanical Properties Of Concrete Short Columns Confined With HRB635 Grade High Strength Steel Bars Under Axial And Eccentric Compression

With the increasing shortage of iron ore resources in the world,the development and application of high-strength and ultra-high-strength steel materials in construction projects are of great significance in improving resource utilization efficiency and promoting building energy conservation and environmental protection.HRB635 grade high strength steel bar is a new type of high strength metal material which is microalloyed by hot rolling process.Compared with heat treatment or cold working high strength steel bar,it has significant advantages of high strength,good ductility,good welding performance and low cost.At present,the current specification only for below 500 MPa and the strength of the steel bar has a regulation.For the steel rebar with yield strength higher than 600 MPa,there are many restrictions due to few investigations.To promote the popularization and application of this new type of high strength steel rebar in construction engineering,this paper mainly focuses on the mechanical behaviour of HRB635 grade high strength reinforced concrete short columns under axial and eccentric compression via experimental study.Relative observations can be drawn as follows:(1)The axial compression tests of 10 short reinforced concrete(RC)columns with HRB635 grade high strength steel bars have been performed in this paper.The results show that the failure mode of short columns with HRB635 grade high strength reinforced concrete under axial compression is similar with that of the axially-loaded RC short columns with normal strength steel rebars.The peak load of the specimen is improved with the increase of the reinforcement ratio of high strength longitudinal bars,stirrup strength and the volume stirrup ratio of high strength stirrup.Increasing the stirrup strength and stirrup ratio can effectively improve the ductility of axially loaded RC short columns.In order to take full use of the strength of HRB635 grade steel rebar,the concrete compressive strength should be higher than 50 MPa.(2)Based on the axial compression test of HRB635 grade high strength steel rebar reinforced concrete short column,the finite element(FE)model of RC columns reinforced with HRB635 grade high strength steel rebars is established by ABAQUS software,and is verified by the test.Following this,systematic numerical research on the effect of the concrete strength,the reinforcement ratio of high strength longitudinal bars,the high strength stirrup ratio and the aspect ratio was conducted.Finally,calculation formulas for predicting the axial compressive resistance of HRB635 grade high strength steel rebar reinforced concrete short columns are proposed.(3)The eccentric compression tests of 14 RC short columns reinforced with HRB635 grade high strength steel bars are conducted.The results show that the failure modes of eccentrically-compressed short columns with HRB635 grade high-strength steel rebars are similar with those of eccentrically loaded short columns with ordinary steel rebars,and the column was finally failed in terms of concrete crumbling located at eccentrically loaded side.In this region,the longitudinal steel rebars could take full use of its yield strength.According to the strain analysis of the cross-section,the plane-section assumption is also adapted to the eccentrically-loaded RC column reinforced with HRB635 grade high-strength steel rebars.Compared to the calculation results predicted by the design code of concrete structures,the eccentric compressive resistances of the tested specimens are observed to hold sufficient safety storage.(4)Based on the eccentric compression test of HRB635 grade high-strength steel rebar reinforced concrete short column,the FE model of eccentrically-loaded RC columns reinforced with HRB635 grade high strength steel rebars is established by ABAQUS software,and its accuracy was verified by test results.Following this,systematic numerical research on the effect of the load eccentricity,the concrete strength,the reinforcement ratio of high strength longitudinal bars,the high strength stirrup ratio and the aspect ratio was conducted.Finally,based on the statistical regression analysis on the experimental and numerical results,the design formulas for predicting the eccentric compressive resistances of HRB635 grade high strength steel rebar reinforced concrete short columns are proposed.