page_title: Barrel vault
section_title: Engineering issues
hierarchical_section_title: Barrel vault / Engineering issues
context_page_description: A barrel vault, also known as a tunnel vault or a wagon vault, is an architectural element formed by the extrusion of a single curve along a given distance. The curves are typically circular in shape, lending a semi-cylindrical appearance to the total design. The barrel vault is the simplest form of a vault: effectively a series of arches placed side by side. It is a form of barrel roof.
  As with all arch-based constructions, there is an outward thrust generated against the walls underneath a barrel vault. There are several mechanisms for absorbing this thrust. One is to make the walls exceedingly thick and strong – this is a primitive and sometimes unacceptable method. A more elegant method is to build two or more vaults parallel to each other; the forces of their outward thrusts will thus negate each other. This method was most often used in construction of churches, where several vaulted naves ran parallel down the length of the building. However, the outer walls of the outermost vault would still have to be quite strong or reinforced by buttressing.
context_section_description: 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 m (15 ft) thick, adding the buttressing strength needed to secure the curved design.
  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.
caption: Pointed barrel vault showing direction of lateral forces.
exif: {}