Imperfection measures of eigen- and periodic modes of axially loaded stringer-stiffened cylindrical shell

Abstract

The influence of initial geometric imperfections in the shapes of eigenmodes and periodic modes on the load-carrying capacity of a steel stringer-stiffened cylindrical shell subject to axial compression is studied. For comparison of the influence of different shapes, the imperfections are normalized by an integral-energy measure, which is considered as an alternative to the commonly applied amplitude. The shell dimensions are chosen out of the set of 24 small-scale specimens tested between 1981 and 1984 at Imperial College in London. Published results of statistical analysis of measured imperfection surfaces of the set are employed for checking their conjectured relationship to the normalization of imperfections by the energy measure. The study is finite element method (FEM)-oriented; the numerical model is checked by application of two FEM codes.

Computational modelling of geometric imperfections and buckling strength of cold-formed steel

“…As it will be shown below an eigenmode of the channel possesses this kind of distortion. Another measure derives from the elastic strain energy hypothetically required to distort the originally perfect structural element into the considered imperfect shape [10][11][12]. Assuming a geometric imperfection w 0 , its energy measure EM (w 0 ) is defined as the square root of the elastic strain energy functional evaluated for w 0 .…”

“…(3). The hypothetic strain energy of a distorted shape can be directly obtained introducing the imperfection as imposed deformation in the linear elastic FEM model Sadovský et al [12]. Even incomplete deformation field can be introduced, e.g.…”

“…15. Note that employing the energy measure, unrealistic amplitudes of imperfections have been reported in the strength studies on post-buckling of thin plates [11] and stringer-stiffened cylindrical shell [12]. Combination of eigenmodes normalised to a certain level of the energy measure can be readily carried out with combination factors following the Pythagoras rule.…”

Frames with unique global and local imperfection in the shape of the elastic buckling mode (Part 1)

“…In these works it was confirmed that the statement that the simple prescription of the amplitude for the imperfection in the shape of the elastic buckling mode is not satisfactory for general applications. The maximum initial curvature as a measure of the hypothetic elastic strain energy governs [4]. The results were used in Czechoslovak Bridge Standard Č SN 73 6205 (1984), cl.…”

Non-linear idealisation error analysis of an aerospace stiffened panel loaded in compression

“…Stiffened panels are essential parts of aerospace structures due to their weight to stiffness ratio. For the safe design of new products it is important to investigate the loading response of these parts and to determine their failure load [1][2][3][4][5][6]. The outcome is crucial for virtual testing during the certification procedure.…”