Barrel Vault - Engineering Issues

Engineering Issues

With a barrel vault design the vectors of pressure result in a downward force on the crown while the lower portions of the arches realise a lateral force pushing outwards. As an outcome this form of design is subject to failure unless the sides are anchored or buttressed to very heavy building elements or substantial earthwork sidings. For example, at Muchalls Castle in Scotland adjacent walls to the barrel vaulted chambers are up to 4,6 meters (15 feet) thick, adding the buttressing strength needed to secure the curved design. Well documented cases exist of the long term stress effects on inadequately laterally supported barrel vaults such as the 17th century church of Guimarei.

The inherent difficulty of adequately lighting barrel vaulted structures has been widely acknowledged. The intrinsic engineering issue is the need to avoid fenestration punctures in stonework barrel vaults. Such openings could compromise the integrity of the entire arch system. Thus the Romanesque medieval builders had to resort to techniques of small windows, large buttresses, or other forms of interior wall cross-bracing to achieve the desired lighting outcomes. In many of the monasteries a natural solution was cloisters which could have high barrel-vaulted construction with an open courtyard to allow ample lighting.

Since 1996 structural engineers have applied Newtonian mechanics to calculate numeric stress loads for ancient stonework barrel vaults. These analyses have typically used a finite element algorithm to calculate gravity induced stresses from the self weight of an arched system. In fact, for structural engineers, analysis of the barrel vault has become a benchmark test of a structural engineering computer model "because of the complex membrane and inextensional bending states of stress" involved.

In terms of comparison to other vaulting techniques the barrel vault is inherently a weaker design compared to the more complex groin vault. The barrel vault structure must rest on long walls creating less stable lateral stress, whereas the groin vault design can direct stresses almost purely vertically on the apexes.