Research On Compressive Performance And Calculation Method Of High Strength Concrete Short Columns Confined By 635MPa High Strength Hot Rolled Steel Bars

With the increasing shortage of iron ore in the world,it is of great strategic significance to facilitate the application and promotion of high strength bars in housing construction and infrastructure to improve the utilization efficiency of iron and steel,save national resource reserves,improve social and economic benefits,and reduce construction costs.In recent years,with the green development policy for the construction industry during the 13 th Five-Year plan as the guidance,more attention has been paid to research and application of high strength bars in China,for example,HRB600 grade high strength bars have been included in GB∕T 1499.2.At present,the application of high strength bars in China generally presents the characteristics of small proportion and low strength compared with that in developed countries such as Europe and the United States.However,due to the lack of systematic experimental data,the application of HRB600 grade high strength bars in concrete structure is relatively rare,so the Code for Design of Concrete Structures(GB50010-2010)didn’t include HRB600 grade high strength bars.Recently,most of the steel bars above 600 MPa in China are made by heat treatment or cold rolling process,and their mechanical properties are limited in practical engineering application.The 635 MPa high strength hot rolled bar is a new type of high strength micro-alloyed metal material by hot rolling process.Compared with heat treatment or cold processing high strength bars,the 635 MPa high strength hot rolled bars have the obvious advantages of higher strength,good ductility and low cost.It is of great importance to the construction industry to promote the upgrading of building materials technology and realize building energy conservation and environmental protection.In order to accelerate the promotion and application of this new type of high strength bars in practical engineering,this paper mainly carries out the relevant experimental research and the relevant calculation method research on the mechanical performance of high strength concrete short columns confined by635 MPa grade high strength hot rolled bars under axial and eccentric compression.The specific research contents and results are as follows:(1)In this paper,axial compression tests of 11 high strength concrete short columns confined by new type of 635 MPa high strength hot rolled bars have been completed.The study shows that the failure mode of the high strength concrete short columns under axial compression confined by the new 635 MPa high strength hot rolled bars is similar to that of ordinary reinforced concrete short columns under axial compression.With the increase in the reinforcement ratio of high strength longitudinal reinforcement,stirrup strength,volumetric ratio of high strength stirrups,and the strength grade of high strength concrete,the peak load of components has increased significantly;increasing the strength of stirrups and the ratio of stirrups can effectively improve the ductility of axially compressed short columns.In order to give full play to the strength of the new type of 635 MPa high strength hot rolled bars,it is appropriate to match them with concrete with strength grade above C50.(2)In this paper,eccentric compression tests of 14 high strength concrete short columns confined with new 635 MPa grade high strength hot rolled bars have been completed.The research shows that the failure mode of the eccentrically compressed short column of high strength concrete confined by new 635 MPa grade high strength hot rolled bars is similar to that of the ordinary reinforced concrete eccentrically compressed short columns,and the final failure mode is the concrete collapse on the eccentric compression side.The results show that the strength of longitudinal bars under eccentric compression is basically fully exerted when the component reaches the peak load.The section strain analysis shows that the plane section assumption is still applicable to the high strength concrete short columns under eccentric compression confined by the new type of 635 MPa high strength hot rolled bars.The comparative analysis combined with the domestic code formula shows that the eccentric load bearing capacity of the specimen is safe compared to the calculated value obtained by the eccentric load bearing capacity formula of short columns provided by the Code for Design of Concrete Structures(3)Based on axial compression performance tests,an analysis model of high strength concrete short columns confined by new 635 MPa grade high strength hot rolled bars has been established with the ABAQUS finite element numerical simulation method and accuracy of the analysis model has been verified.The study on the influence of parameters such as the strength grade of high strength concrete,the ratio of high strength longitudinal reinforcement,the ratio of high strength stirrups,and the aspect ratio on its force and deformation properties has been systematically carried out.Finally,based on the Code for Design of Concrete Structures and statistical regression analysis of experimental and simulated data,a calculation method suitable for evaluating the bearing capacity of high strength concrete short columns under axial compression confined by new 635 MPa high strength hot rolled bars has been proposed.(4)Based on eccentric compression performance tests,an analysis model of high strength concrete short columns hot under eccentric compression confined with new635 MPa grade high strength hot rolled bars has been established with the ABAQUS finite element numerical simulation,and accuracy of the analysis model has been verified.A systematic study on the influence of parameters such as eccentricity,strength grade of high strength concrete,high strength longitudinal reinforcement ratio,and volumetric stirrup ratio of high strength stirrups on its force and deformation properties has been carried out.Finally,based on the statistical regression analysis of eccentric compression tests and simulation data,a calculation method suitable for evaluating the eccentric compression bearing capacity of high strength concrete short columns confined by new 635 MPa high strength hot rolled bars has been proposed.