NONCLASSICAL EFFECTS IN NONLINEAR-ANALYSIS OF PRETWISTED ANISOTROPIC STRIPS

The literature on classical analysis of anisotropic beams assumes that all 1D ''moment strain'' measures (i.e. twist and bending curvatures) are of the same order of magnitude, resulting in a linear cross-secti onal analysis. The present paper treats the situation in which one or more of the 1D moment strain measures may be larger than the other(s), resulting in a non-linear cross-sectional analysis. This type of non- classical analysis is needed, for example, in problems where the trape ze effect is important, such as in rotor blades. As a precursor to com plicated non-linear sectional analysis of arbitrary cross sections, a non-linear sectional analysis is presented for an anisotropic strip wi th small pretwist, based on the dimensional reduction of laminated she ll theory to a non-linear one-dimensional theory using the variational -asymptotic method. Results obtained from this strip-beam analysis are compared with available theoretical and experimental results for a pr oblem in which the trapeze effect is important. In order to demonstrat e the usage of the results in the analysis of structures made of an ar bitrary geometrical combination of pretwisted generally anisotropic st rips, a closed-form expression is derived for the torsional buckling o f a column with a cruciform cross section. (C) 1998 Elsevier Science L td. All rights reserved.