| The overall instability is an important failure mode of the steel beams. The buckling modes and stability capacities are significantly influenced by the variations in the section shape, the type of loading and condition of support. The researches of the overall instability of supported beam and cantilever beam are already very mature at home and abroad, but the researches on the overall instability of the mono-overhanging beam both in experimental research and theoretical analysis is obviously insufficient. The code among different countries also did not give reliable stability capacity formula, Chinese code only indicaded that we should take measures to strengthen support at the torsional capacity when giving the formula of overall stability coefficient of cantilever beam. Actually ,the proposed formulas for calculating the critical moment of overall stability of the biaxial symmetry I-shaped mono-overhanging beam mostly ignored the influence of the loading position and the overhanging length ratio.Therefore the overall stability behavior of the biaxial symmetry I-shaped mono-overhanging beam still need to be further investigated.According to the mechanical principle,the mono-overhanging beam can be simplified as a simply supported beam.This paper has derived the formula of critical moment of simplified model by Raykeigh-Ritz energy method, and compared the results between the ANSYS finite element analysis and formula of critical moment of simplified model,the results showed good agreement. It had indicated that the ANSYS finite element model can reflects the overall instability behavior of the thin-walled I-shaped mono-overhanging beam, and it's formula of critical moment can be replaced by simply supported beam when the control section of mono-overhanging beam is located in the simply supported part.Using the results of ANSYS finite element analysis, large amounts of finite element parametric analysis were performed for the biaxial symmetry I-shaped mono-overhanging beam. This paper obtained the influence law of various parameters on the critical moment of I-shaped mono-overhanging beam by changing the section dimensions,the overhanging length ratio, the load position, the torsional stiffness coefficient,the span of simply-span and so on.Based on the ANSYS finite parametric analysis results and the formula of critical moment and overall stability coefficient of supported beam in Chinese code, the investigation on the ratio of the critical moments between the biaxial symmetry I-shaped mono-overhanging beam and the supported beam M c /M ce or M d /M de were conducted.It is found that the relationship between the ratio of M c /M ce or M d /M de and the coefficients of torsional stiffness of the dominative segment K agreed with quadratic parabola.This paper has derived the formula of critical moment of the mono-overhanging beam which acted by concentrated load and simply supported load by curve fitting method.This formula considered the overhanging length,load scale and three load positions which inconcloded the top-flange,shear and lower-flange. |
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