Nth-order stiffness sensitivities in structural analysis

This paper presents a general expression for the Nth-order stiffness sensitivities in linear elastic frames. It is based on modelling the structure as being composed of unimodal elements. It is shown that the sensitivity of the structural response to the variation of the stiffness of an arbitrary component depends only on the corresponding elemental displacements. These are the nodal displacements due to nodal element loads applied to the structure at the end nodes of the considered element. Therefore, on the basis of one structural analysis we obtain the sensitivity of the structure to the variation of a given stiffness, to any order and for all loading conditions. Partial derivatives with respect to several element stiffnesses are obtained from the elemental displacements of the considered elements. The method is equally applicable to more general finite element models. It requires, however, the preliminary decomposition of the finite elements into their unimodal components.