Statics of sail vaults under self-weight and support displacements: the effect of bond pattern

The two primary bond patterns for constructing sail vaults are the ring-based and the dovetail bonding. Historical sources often note that these patterns were recommended for different approximate span ranges: the dovetailed pattern for smaller spans (below approximately 3–4 m), and the ring-based pattern for larger spans, up to around 5 m. The present study investigates the mechanics of square-bay sail vaults using discrete element modelling, considering the two bonding patterns in vaults with representative spans, and examines their response to self-weight and the two most common types of quasi-static support displacements, with the aim to explore the mechanical background of the empirical span rules. The findings show that the masonry pattern is a primary governing parameter that controls the internal force distribution and thrust trajectories that can be observed within the structure. However, from mechanical point of view neither masonry pattern can be considered inherently more efficient than the other: instead, the historical rule of thumb regarding the preferred bonding technique should be interpreted as being due to primarily constructional considerations, such as the relatively simple freehand laying of the dovetailed pattern for smaller spans, and the ease to locally increase the stress-resisting capacity in the ring pattern through thickening of the concentric courses at mechanically critical regions.