The Structural Engineer > Archive > Volume 64 (1986) > Issues > Issue 13 > Stability Fundamentals in Relation to Masonry Arches
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Stability Fundamentals in Relation to Masonry Arches

When the voussoirs of a masonry arch are idealised as a set of rigid blocks abutting against each other, classical energy and virtual work principles commonly used in structural analysis are not valid for determining either equilibrium or stability. This paper establishes that stable equilibrium is achieved through a V-shaped, rather than a U-shaped, curve of potential energy against displacement. The possibility that such a form of equilibrium may exist is not mentioned in textbooks or papers on structural analysis, as far as the author is aware. Yet recognition of this form of equilibrium is essential to the understanding of masonry arch stability, since the use of the second differential of potential energy to investigate stability gives the incorrect answer that all arches except very thick ones are unstable even when subject to just their own self-weight. Professor A. Jennings