Raasch challenge for shell elements

The Raasch challenge problem of a curved strip with a tip in-plane shear load is examined in an attempt to better understand bow certain shell element features affect its solution. Various shell element formulations are used in the assessment in an attempt to define any inherent pathological problems of the shell finite elements or the problem itself. Six different flat shell elements and two solid brick elements are assessed by this problem, and the findings are very surprising. Selected aspects of shell finite-element development that are relevant to this problem are briefly described. These aspects are the inclusion of transverse shear flexibility in the element formulation, the addition of drilling degrees of freedom, and the realignment of shell surface normals. Shell elements without transverse shear flexibility appear to converge to an appropriate value (i.e., 5% stiffer than the three-dimensional solution). Shell elements with transverse shear flexibility do not appear to converge.