| Aluminum alloys have a lot of advantages,such as high strength,low density,excellent corrosion resistance,ease of maintenance and utilization.The tensile strength of 6000 series al-alloys is close to or even higher than that of Q235 steel;however,the density is only about one-third of the latter.Therefore,the aluminum alloy components have a broad range application and development prospects in engineering and building structures.At present,the relevant provisions of the current Chinese code for the design of aluminum structures GB 50429-2007 are mainly formulated based on the test data of 6061-T6 aluminum alloy members.The applicability of the 6082-T6 aluminum alloy members still needs to be further explored.Compared with the research on the stability of aluminum alloy columns under axial compression,it is still in the initial stage in the field of eccentrically loaded columns and bending members,which need to be supplemented by the experimental analysis and theoretical research.In view of the above problems,this paper performed the experimental and numerical research on 6082-T6 aluminum alloy members subjected to eccentrical compression and bending moments.The failure modes of aluminum alloy members were summarized,and the influence of factors such as slenderness ratio,section size and eccentricity on the ultimate strength of members was studied.As for the theoretical analysis,the accuracy verification and reliability analysis of Chinese code were carried out,and the relevant factors were modified for the calculation formula of the ultimate strength.In addition,the error and reliability analysis of several foreign design provisions were carried out,and compared with the Chinese code,to provide the reference for the revision of the latter.The specific research contents are as follows:(1)Experiments and simulations of the eccentrically loaded specimensThe buckling behaviors of 59 pin-ended 6082-T6 aluminum alloy specimens,including 13 rectangular hollow section(RHS)columns,16 angular section(L-type),11 square hollow section(SHS)columns and 19 circular hollow section(CHS)columns,were investigated,and the ultimate strengths and deformation capacities of the specimens were recorded.The specimens with larger slenderness ratios were more likely to fail by local buckling,while those with smaller slenderness ratios failed by overall buckling.The finite element(FE)models of the tested columns were developed using the non-linear finite element analysis(FEA)software ABAQUS.The simulation errors of the ultimate strengths for most members were less than 5%,and the load-displacement(strain)curves were in good agreement with each other;the influence of the initial bending amplitude and mesh size on the simulation results was analyzed.By carrying out parametric analysis,3850 simulation results were obtained.With the increase of the slenderness ratios,the slope of the end axial force-bending moment curve becomes lower,and the instability failure of the specimens changed from the end axial force control to the end bending moment control.(2)Experiments and simulations of the bending specimensThe bending tests of 47 aluminum alloy specimens were carried out,including 10 SHS members,10 RHS members,10 I-section(H-type)members and 17 CHS members,and the corresponding supports and loading devices were designed according to the different section types.The deflections and strain were recorded along with the bearing capacity of the bending members at the mid-span and loading points,and the rotation capacity of the end supports and failure modes were also investigated.The RHS and SHS specimens with smaller slenderness ratios and the CHS specimens with larger D/t ratios were prone to fail by local buckling;on the contrary,the components were prone to fail by strength failure.All the H-type specimens failed by flexural-torsional buckling.The FE models of the bending specimens were developed using ABAQUS;the errors of the ultimate strength were less than 5% and the simulated load-displacement(strain)curves were almost coincided with the tested curves.The influence of the width-to-thickness ratios,diameter-to-thickness ratios and slenderness ratios on the ultimate strength and failure modes of the bending members was evaluated and the parameter analysis was performed with 2400 simulated results obtained.The ultimate strenghts of RHS,SHS and CHS components decreased with the increase of the section flexibility coefficient,while the ultimate strenghts of H-type components decreased with the increase of the flexural stability relative slenderness ratio.(3)Comparison and verification of the design provisions for the ultimate strengthThe design provisions from the Chinese code GB 50429-2007,European code Eurocode 9 and American code AA-2015 were compared with each other.Both DSM and CSM were introduced into the calculation of the ultimate strength for aluminum alloy specimens;the design forlumas of eccentrically loaded columns were proposed based on the DSM and CSM,with the consideration of effective centroid migration.Based on the experimental and simulated data obtained from this paper,the applicability of the five design provisions was evaluated and compared with each other.The calculation results of the ultimate strengths for Chinese code were conservative,with an average error of about 25% and 30%,respectively.Based on the evaluation results,the correlation coefficients of the formulas in Chinese code were modified,and the accuracy of the formulas was improved by 10% to 40%.(4)Reliability analysis of the design provisions for the aluminum alloy specimensThis paper has collected all the test results of aluminum alloy specimens published in China until 2019,and established an experimental database containing different alloys,section types and load conditions.The statistic parameters of the material strength and geometrical properties were calculated from the database.By establishing the probability density histograms and inverse cumulative distribution function(CDF-1)plots,this paper has determined the optimal distribution types of the model errors for different design provisions,and the load random variables and load combinations of Chinese,European and American codes were also collected.For evaluating the reliability levels of the aluminum alloy members under different loading conditions,a performance function was proposed,which considers the distribution types of model errors,material strength,geometrical properties,load combinations and other factors.According to this function,the reliability indices of the above 5 design provision were calculated and compared with each other,and a reliability sensitivity analysis of the basic variables was performed.This paper has discussed the adjustment of the load combinations in the 01 th edition and the 18 th edition of “Unified standard for reliability design of building structures” and evaluated the influence of the adjustment content on the reliability results of the aluminum alloy specimens.In the end,some suggestions were put forward to modify the parameters of the Chinese code,so that the revised formula can meet the target reliability indices. |
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