The Effect of Boundary Conditions on the Behaviour of Pointed Masonry Barrel Vaults: Late Gothic Cases in Scotland

Barrel vaults provide effective fire-proof roofing in historic churches, castles, cloisters or halls that look for simple and utilitarian aesthetics, as long as they are strongly connected to sturdy lateral walls and transverse gables, conditions that limit their possibilities for spatial expression. A study of the effect of these conditions was carried out on the pointed vaults of a characteristic group of 15^thcentury Scottish churches. Following earlier measured surveys that showed remarkable geometric integrity, 1/15-scale models of a representative form were made in reinforced plaster that could delay the cracks propagation enough to be monitored. Only the shell was considered, leaving the effect of ribs or diaphragms that hold the heavy flagstone roof for further study. The model was subject to symmetric and asymmetric horizontal spread, which simulated the insufficient containment of not very stiff walls, but included the effect of gable end walls. Cracks formed invariably at an early stage (3% of the span spread), propagating more rapidly and causing early failure at a symmetrical spread (15% of span), while the asymmetrical spread produced diagonal crack patterns across the vault at 33% of the span. Gables provided more stiff areas but eventually caused local detachment at the spread point, at only 5% of the span, with cracks propagating to the back wall and at a higher rate when a less stiff gable was included(13% of span). The results validated an FE model that provided further insight to the performance of the type at displacement and settlement, as exemplified in the case of Bothwell church in Scotland.

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