ESDU STRUCT 01.01.08
Local instability of struts with flat sides.
Abstract:ESDU Struct 01.01.08 provides a graph from which the stress for initial local buckling of the web or flange of closed or open section struts can be obtained. Plasticity is taken into account by representing the stress-strain curve of the material by the expressions given in ESDU 76016, which require a material characteristic, m, and the stress, fn, at which the tangent modulus is half the elastic modulus of the material in compression. The graph plots the ratio of the buckling stress to fn for various values of m against a parameter involving the buckling stress coefficient, the width of the appropriate side and the modulus of elasticity of the material. The buckling stress coefficient is defined as the square of the width to thickness ratio of the appropriate side factored by the ratio of the critical stress to the tangent modulus of the material. Superimposed on those curves are two sets of lines plotting the root of the ratio of fn to the modulus of elasticity, one for constant thickness to width ratio of the web and a similar set for the flange. That auxiliary set of lines allows a rapid evaluation of the abscissa from which the buckling stress is readily obtained. The curves apply to struts whose length exceeds four times the larger width of the section. For open sections it is assumed the lip will prevent the web buckling sideways. Generally there will be an interaction between different modes of buckling and ESDU 76023 and ESDU 77030 treat such effects. However, where a local mode is known to predominate, the method gives good estimates of the buckling stress. A worked example illustrates the use of the curves. For a panel with Z-section stiffeners, ESDU 71014 treats local buckling including the influence of the plate. ESDU 90002 introduces a computer program that treats flexural and local modes of buckling and inter-rivet buckling.
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