| In order to solve the problem that the upper chords of semi-wear truss bridges’ out-of-plane instability,the stability bearing capacity of the loaded upper chords and the effective length coefficient were studied by means of theoretical analysis,experimental study and numerical analysis.The specific research contents and achievements are as follows:(1)The constitutive relation curves of 53 domestic 6061-T6 and 90 domestic 6082-T6 aluminum alloys are obtained by analysing experimental results.Based on experimental datas,the constitutive relation model of aluminum alloy material and the applicability of Steinhardt hypothesis are analyzed.The results show that the constitutive relation of domestic 6061-T6 and 6082-T6 aluminum alloy material can well obey the Ramberg-Osgood model,and according to Steinhardt hypothesis,the value of n is 24 and 26.(2)This paper compares the differences between the codes of China,Europe,Amercia and Germany by means of theoretical analysis.The aluminum alloy grades and the parameters are different in the four codes.Chinese,European and Amercian design system adopt the ultimate bearing capacity method.And German design system adopts the allowable stress method.The calculation formula of the stability bearing capacity is composed of axial and bending,but the expressions of the two are different.The influencing factors of the stability bearing capacity of the four countries are eccentricity,slenderness ratio,stability coefficient and influence coefficient.According to the difference between the four countries’ design systems,the bridge structure models of four kinds of load combinations are established by Midas Civil software.According to the results of the model analysis,the safety of the four countries’ design systems are evaluated.The results show that the results of the Amercian results is safe for the compression and bending members with small bending moment and axial compression.The Chinese results is safe for the bending members.(3)The nonlinear analysis of the compression and bending members is carried out by ANSYS finite element software.Compared with the experimental results and finite element results,the finite element results are in good agreement with the experimental results.519 compression and bending members are analyzed by using finite element method.According to the results of finite element analysis,the calculating formulas of compression and bending members of China,Europe,Amercia and Germany is verified and revised by using correlation curve method.And the four national results are compared.The results show that the calculated formulas of Chine and Europe can be used to calculate the stability bearing capacity of 6082-T6 compression and bending members.But the calculation results are conservative.The Amercian and German formulas can not be applied to the compression and bending members’ stability bearing capacity that out-of-plane buckling with small eccentricity.The revised four national normative formulas meet the requirement of stability bearing capacity and the results are more reasonable.(4)The modal analysis and nonlinear analysis of the semi-wear truss bridge are carried out by using ANSYS finite element software to determine the first-order modal buckling form,the waveform state and the upper chords axial forces of the bridge structure under the limit state.According to axial force of upper chords,the chords effective length coefficient is calculated by Euler formula.And the "port engineering code for design of steel structure","steel structure of railway bridge design specifications" and "waterway engineering design code of steel structure" is compared with the calculation results.The results show that the finite element nonlinear analysis method can be used to calculate the effective length coefficient of the upper chords on semi-wear truss bridges of aluminum alloy.From the safety point of view,the results of "water transport engineering steel design code" is safer. |
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