A study of the saddle stresses arising from the support of a cylindrical vessel

The design method widely used for the support of cylindrical vessels is that contained in BS 5500¹ which is based on the work of Zick² published in 1951. In recent years, however, the theoretical analysis of this problem has received some attention,^3–7 thus enabling the vessel stresses and displacements to be determined for supporting saddles of various degrees of flexibility. In this paper the saddle itself is examined, 1) experimentally, using photoelasticity, and 2) analytically by the shell analysis of refs^5–7, together with a Finite Element approach. It is found that the theoretical approach used to determine saddle stresses is very sensitive to— the type of finite element used for the saddle, and the boundary assumption at the saddle base. From a general stress analysis point of view, the paper should provide a warning to designers that the results obtained from finite element analyses always contain the above inherent problems. A comparison with the photoelastic results enables this to be studied. In particular the agreement between the theoretical and experimental approaches lends credence to the analytical approach used in refs^5–7 and to the value of an optimum design approach for the vessel and its support.