We study the structural performance of flat vaults, depending on the patterns of
voussoirs. For this purpose, we propose three archetypes, derived from the 18th–19th
century literature on stereotomy, with fit simplifications.
The ultimate structural answer of these models are evaluated, searching
numerically for statically admissible loading conditions by means of an enhanced
version of the thrust network analysis, assuming failure occurring by joints’ opening,
crushing or sliding, while voussoirs remain rigid.
The considered enhancements allow one to better capture the contact forces
acting on the joints and to define consistently the safety factor of the structure. They
are based on the introduction of additional partial branches in the thrust network
that represent actions internal to the voussoirs and are essential to describe, at least
in some cases, their rotational equilibrium, which is neglected by the standard
analyses.
The three examples are compared by superposing their domains of statically
admissible loadings, represented in terms of vertical uniformly distributed load
vs. thrust. Our findings support but partly some of the conjectures presented in
the 18th century and later literature, especially because of a plate effect
that can be observed at the corners of these structures. They also allow us
to classify flat vaults according to the local shape of the force network, as
elliptical, parabolic or hyperbolic, thus opening to a new interpretation of their
nature.