A principle of virtual power-based beam model reveals discontinuities in elastic support as potential sources of stress peaks in tramway rails

This paper addresses the question to which extent the stiffness of an elastic foundation in general, and of a discontinuity occurring in the foundation in particular, affects the stresses to which a beam resting on such a foundation is exposed to. This is particularly relevant for tramway rails, where foundation discontinuities may be generated in the course of maintenance works. In the presented work, the underlying mathematical framework was derived based on the principle of virtual power, using a suitable virtual velocity field and a foundation-related traction force vector as input quantities. The resulting mathematical expressions for the virtual powers performed by the internal and external forces were approximated based on Finite Element discretizations, and eventually solved correspondingly, in the format of sequential Finite Element analyses. Numerical studies, performed on a tramway rail-shaped beam, have confirmed that foundation discontinuities indeed induce substantial increases in the stress tensor components, when moving from regions of a high-stiffness foundation to regions of a low-stiffness foundation; as it may occur if specific sections of the tramway network get renewed.

Variational formulation of boundary-value problems

This chapter discusses a variational formulation of boundary value problems in small deformation solid mechanics. It begins by introducing the important principle of virtual power, and shows that it encapsulates Cauchy’s traction law, and the local form of the basic balance of forces (equation of equilibrium), and the local from of the balance of moments (symmetry of the stress). Since the principle of virtual power encapsulates both the equation of equilibrium and the Cauchy relation for tractions, it can be used to formulate and solve boundary-value problems in solid mechanics in a variational or weak sense. Specifically, it is shown how the displacement problem of linear elastostatics may be formulated variationally using the principle of virtual power.