The linear elastic stress analysis of curved pipes under generalized loads using a reduced integration finite ring element

This paper consists of a linear elastic stress analysis of curved pipes having all the possible boundary conditions in structural engineering and submitted to a generalized in-plane or out-of-plane loading. A semi-analytic displacement formulation ring element was developed, where simple first-degree polynomials were used to interpolate the global shell displacements along the longitudinal direction, and Fourier series were used along the meridional direction. The deformed shape of the curved pipe results from the superposition of the beam-type displacement to that of a toroidal shell. For the first case, the curved pipe was considered as being a short thin-walled straight beam element joining two nodal sections. In this case, as the pipe element is not curved, it is natural to consider that the transverse section undergoes no ovalization or warping. A C0-continuity reduced integration beam element was adopted for this purpose, leading to a simple and economic definition for the stiffness terms. In the second case, the displacement field was assumed to result from a stressed toroidal shell, where the transverse section could ovalize and warp. The stiffness terms following these assumptions are combined with those of the straight beam to give the complete stiffness matrix. This element has the important advantage of generating a zero stress field along the curved centroidal line when submitted to pure in-plane bending and, consequently, to the satisfaction of the ‘patch test’