In this paper a constitutive equation for masonry arches is defined an
d its main properties are proven; in this equation to each pair of gen
eralized strains (epsilon, kappa), with epsilon the extensional strain
and kappa the curvature change of the centre line, is assigned the pa
ir of generalized internal forces (N, M), where N is the normal force
and M the bending moment. Subsequently, the collapse of masonry arches
is characterized and the static and kinematic theorems proven. Finall
y, a method for determining the collapse load in the case of circular
arches subjected to their own weight and a vertical point load applied
at a point of the extrados is presented. The results obtained, of int
erest in some applications, are summarized in a series of graphs.