Performance Study Of Concrete Compression Member Reinforced With Grade 500MPa Steel Bar

Concrete structure is the most widespread structural style at present in our country. But strength grade of steel bar applied in concrete structure in our country is universally 1-2 grades lower than that in overseas.This directly causees crowded reinforcing bars in concrete members,construction difficulty,oversized steel bar amount,and the high energy and resources consumption,which run counter to "the sustainable development" policy our goverment advocates at present.In recent years in our metallurgical industry,HRB500 steel bar was developed by rare elements(such as vanadium et) addition,and 500MPa level ultra-fine crystal grain steel bar was newly exploited out through temperature and rolling conformity technology,which has no or fewer rare element.HRB500 steel bar has been included in " Hot rolled ribbed steel bars for the reinforcement of concrete "(GB1499-1998), but because the lack of comprehensive and systematic scientific effort,especially seriously insufficiency of fundamental experiment study,500MPa grade steel bar has not been included in the "Concrete structure Design Code"(GB50010-2002),which immediately influence the application of 500MPa grade steel bar in actual project.In this paper,for the purpose of 500MPa grade steel bar application in concrete compression members,a total of 32 axially compressed and nine eccentrically compressed 500 MPa grade steel bar reinforced concrete column tests were conducted, compression performance study was carried out,axial compression stress-strain curve and numerical simulation of eccentrically compressed column were analyzed according to test results,the design suggestion of 500 MPa grade steel bar used in reinforced concrete compression member was proposed,and the application analysis of HRB500 steel bar pilot project was completed in accordance with the above proposal.The main content is as follows:1.Through test of axially compressed concrete column reinforced with 500 MPa grade steel bar,the influence of concrete strength,longitudinal reinforcement ratio, transverse stirrup and longitudinal steel strength on axially compressive performance was analyzed,the relationship between concrete peak strain,concrete peak stress and concrete strength,longitudinal reinforcement ratio was discussed,the result shows that:①With the increase of concrete strength,longitudinal reinforcement ratio and volume ratio of stirrup hoop,concrete peak strain of axially compressed column is significantly increased,and can be reached above 0.002.Within the longitudinal reinforcement ratio scope commonly used in concrete compression member and stirrup situation ruled by code,the concrete compressive peak strain is at the range of 0.0022 to 0.0026,and the compressive strength of 500MPa grade steel bar can be fully developed.②The specimen bearing capacity was calculated and analyzed in accordance with the formula of axially compressed column in Chinese existing code,the average ratio of test value to calculation value are 1.08(strength of concrete and steel bar is taken as the mean value of test) and 1.24(strength of concrete and steel bar is taken as the characteristic value) respectively,which indicates that calculated formula is in a certain of security.2.According to concrete stress-strain curves of axially compressed column obtained in tests,through the analysis of curve characteristic point and modification of concrete stress-strain curve in Appendix C(Chinese Code),a concrete stress-strain curve equation in consideration of longitudinal reinforcement and transverse stirrup was derived,of which calculation results are in good agreement with test results,and can be used as reference of nonlinear analysis of concrete structure and members.3.Through test of eccentrically compressed concrete column reinforced with 500 MPa grade steel bar,the influences of eccentricity and longitudinal steel ratio on the specimen lateral deflection,concrete strain at compression edge and longitudinal reinforcement strainwere analyzed,result shows consistent performance with common eccentrically compressed reinforced concrete column.The specimen bearing capacity were calculated according to Chinese existing code,the average ratio of test value to calculated value is 1.18,which indicates that calculated formula is in a certain security.4.On the basis of experimental study of eccentrically compressed concrete column reinforced with 500 MPa grade steel bar,a nonlinear analysis procedure based on Matlab about eccentrically compressed column was worked out,numerical simulation tests of eccentrically compressed concrete column reinforced with 500 MPa and HRB335 grade steel bar respectively were conducted,the impact on second-order effects of eccentricity,slenderness ratio,concrete strength and longitudinal steel ratio were comparatively analyzed,results show that the law of second-order effects of concrete column reinforced with 500 MPa grade steel bar is basically the same with that reinforced with ordinary steel bar.Second-order effects of simulation test specimen were calculated in accordance with Chinese,American and European codes, the calculation results primarily agree with each other,and it can be induced that second-order effects calculation of eccentrically compressed concrete column reinforced with 500 MPa grade steel bar can be designed according to the existing Chinese code provision,and of essentially the same security degree with that reinforced with HRB335 grade steel bar.5.Through the above experiment study and analysis,the design value of compressive strength(f'_y=f_yk/γ_s=500/1.1≈450MPa) and design suggestion for use of 500 MPa grade steel bar in reinforced concrete compression member was proposed,according to above proposal,HRB500 grade steel bar pilot project was designed,a comparative analysis of steel consumption was conducted with that use HRB335 and HRB400 grade steel bar,the results indicate that:①By replacing HRB335 and HRB400 grade steel bar with HRB500 grade steel bar, the reinforcement amount can be reduced under certain conditions,the steel bar crowded phenomenon can be improved in node,beam and column etc.of frame structure,the project quality can be reformed,and better social economy progress can be received.②In order to more effectively promote the use of 500 MPa grade steel in project structure,the calculating method or provisions of crack width and the minimum reinforcement in existing code need to be improved and perfected,and a project basis was provided for 500 MPa grade high strength steel bar in Chinese "concrete structure design code".This article research obtained the State Natural Sciences Foundation(the project authorization number:50578148) and national 863 plans(project number: 2004AA33G050) subsidization.