| Parallel twin-arch with braces is a common structural form used in long-span bridges and building structures.Because of the constraint effect of transverse braces,the buckling behavior of parallel twin-arch is quite different with the single arch,and the critical buckling load are significant affected by the stiffness and layout of the transverse braces.In order to study the influence of the parameters of transverse braces on the out-of-plane buckling behavior of the parallel twin-arch,and to establish the calculation method of the out-of-plane elasto-plastic critical buckling load,the out-of-plane buckling behavior of circular double twin-arch subjected to uniform radial load is studied systematically by means of experimental research and finite element parametric analysis in this paper.The specific research works are as follows:(1)Six groups of parallel twin-arch specimens with different stiffness ratios between transverse brace to main arch rib are designed,and a special five-point radial loading device is also produced and the out-of-plane elastic-plastic stability loading tests are carried out subsequently.The in-plane and out-of-plane load-displacement curves,and load-strain curves of the key sections of the main arch ribs and transverse braces are tracked and recorded during the whole process of loading.According to the tested results,the influence of the stiffness ratio between the transverse brace to the main arch rib on the out-of-plane stability of parallel twinarch specimens is studied.It is found that the out-of-plane stability of parallel twin-arch increases with the increase of the stiffness ratio of the transverse brace to main arch rib.When the ultimate load is reached,the strains of the cross-section of the ends and crown of the arch is the largest,indicating that the arch ends and arch crown are the positions where the buckling failure first occurs.(2)Considering the effects of the initial geometric imperfections and material nonlinearity,the finite element software ANSYS is used to simulate and analyze the experimental specimens.The calculated out-of-plane and in-plane load-displacement curves,load-strain curves of each sections are compared with the tested counterpart.The comparison results show that the FE results are in good agreement with the experimental one,and the average error of these two methods is less than 3.6% as respect to ultimate bearing capacity of the specimens,which verifies the accuracy of the finite element model.(3)The parameters of more than 1000 groups of composite arch models with different the transverse braces factors are analyzed by using finite element software.Considering the geometric initial defects of main arch ribs,the ratio of rise to span and slenderness,the influence of the stiffness ratio of the transverse braces to the main arch,the number of braces,the height of bridge gates and the length of the transverse braces on the out-of-plane stability of the parallel twin-arch is studied.The results show that the stiffness ratio of the transverse braces to the main arch and the height of bridge gate have greater influence on the out-of-plane stability of parallel twin-arch,followed by the number of braces and the length of braces.(4)Based on the results of parametric analysis and considering the influence of transverse braces,the formula for calculating the factor of buckling length to the height of bridge gate is fitted by referring the elastic-plastic stability bearing capacity design formula of parallel twin-arch in German steel structure code.And then the calculation method for out-ofplane bearing capacity of circular parallel twin-arch considering the influence of transverse braces is obtained. |
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