Flying buttress

An early design of the flying buttress (c.1170) at the eastern end of the Basilica of St Remi in Reims

The flying buttress (arc-boutant, arch buttress) is a specific form of buttress composed of an arched structure that extends from the upper portion of a wall to a pier of great mass, in order to convey to the ground the lateral forces that push a wall outwards, which are forces that arise from vaulted ceilings of stone and from wind-loading on roofs.^[1]

The defining, functional characteristic of a flying buttress is that it is not in contact with the wall it supports, like a traditional buttress, and so transmits the lateral forces across the span of intervening space between the wall and the pier. To provide lateral support, flying-buttress systems are composed of two parts: (i) a massive pier, a vertical block of masonry situated away from the building wall, and (ii) an arch that bridges the span between the pier and the wall — either a segmental arch or a quadrant arch — the flyer of the flying buttress.^[2]

History

The flying buttresses of the Washington National Cathedral.

As a lateral-support system, the flying buttress developed in the Gothic period (12th–16th c.) of architecture, yet it is described in the Tanakh (Hebrew Bible) as part of the design of a new temple (Book of Ezekiel 41:6, 7); the architectural precursors of the flying buttress derive from Byzantine architecture and Romanesque architecture, in churches such as Durham Cathedral, where arches transmit the lateral thrust of the stone vault over the aisles; the arches were hidden under the gallery roof, and transmitted the lateral forces to the massive, outer walls. By the decade of 1160, architects in the Île-de-France region were employing similar lateral support systems, with longer arches of finer design, which run from the outer surface of the clerestory wall, over the roof of the side aisles (hence visible from outside) to meet a heavy, vertical buttress rising above the top of the outer wall.^[3]

The advantage of such lateral-support systems is that the outer walls no longer need to be massive and heavy in order to resist the lateral-force thrusts of the vault. Instead, the wall surface could be reduced (allowing for larger windows, glazed with stained glass), because the vertical mass is concentrated into external buttresses. The design of early flying buttresses tended to be heavier than required for the static loads to be borne, e.g. at the Chartres Cathedral (c. 1210) and around the apse of the Basilica of St Remi, which is an extant, early example in its original form (ca. 1170).^[4] Later architects progressively refined the design of the flying buttress, and narrowed the flyers, some constructed with one thickness of voussoi (wedge brick) with a capping stone atop, e.g. the cathedrals of Amiens, Le Mans, and Beauvais.

The architectural design of Late Gothic buildings featured flying buttresses, some of which had flyers embellished with crockets (hooked decorations) and sculpted figures set in aedicules (niches) recessed into the buttresses. In the event, the architecture of the Renaissance eschewed the lateral support of the flying buttress in favour of thick-wall construction. Despite its disuse for function and style in construction and architecture, in the early 20th century, the flying-buttress design was revived by Canadian architect William P. Anderson to build lighthouses.^[5]

Construction

Architectural drawing of the type of flying buttress, by Villard de Honnecourt, used in the cathedral at Notre-Dame de Reims.

Given that most of the weight-load is transmitted from the ceiling through the upper part of the walls, the flying buttress is a two-part composite support that features a semi-arch that extends to a massive pier far from the wall, and so provides most of the load-bearing capacity of a traditional buttress, which is engaged with the wall from top to bottom; thus, the flying buttress is a lighter and more cost-effective architectural structure.

To build the flying buttress, it was first necessary to construct temporary wooden frames, which are called centring. The centering would support the weight of the stones and help maintain the shape of the arch until the mortar was cured. The centering was first built on the ground, by the carpenters. Once that was done, they would be hoisted into place and fastened to the piers at the end of one buttress and at the other. These acted as temporary flying buttresses until the actual, stone arch was complete.^[6]

A flying buttress supporting a wall at Chaddesley Corbett.

Moreover, because the flying buttress relieves the load-bearing walls of excess weight and thickness, by way of a smaller area of contact, the wall has a greater surface area in which to install windows, as in the design of a religious buildings, e.g. church, basilica, and cathedral. In the design of Gothic churches, two arched flyers were applied, one above the other, in which the lower flyer (positioned below the springing point of the vault) resists the lateral-thrust forces of the vault, whilst the upper flyer resists the forces of wind-loading on the roof.^[7] The vertical buttresses (piers) at the outer end of the flyers usually were capped with a pinnacle (either a cone or a pyramid) usually ornamented with crockets, to provide additional vertical-load support with which to resist the lateral thrust conveyed by the flyer.^[8]

Remedial support application

Another application of the flying-buttress support system is the reinforcement of a leaning wall in danger of collapsing, especially a load-bearing wall; for example, at village of Chaddesley Corbett, the practical application of a flying buttress to a buckled wall is more practical than dismantling and rebuilding the wall.

Gallery of flying buttresses

Flying buttress at Lincoln Cathedral, England  Flying buttress at Saint-Petrus-en-Pauluskerk; Ostend, Belgium  Flying buttresses at Bath Abbey; Bath Abbey, Bath, Somerset, England;

See also

• Buttress
• Cathedral architecture
• Flying arch
• Gothic architecture
• Seismic retrofit

Notes

1. A Dictionary of Architecture, James Stevens Curls, Editor. 1999:Oxford. pp. 113–114.
2. For the functional mechanics of the flying buttresses, see "Chartres Cathedral: A Reinterpretation of its Structure", by Alan Borg and Robert Mark, The Art Bulletin, Vol. 55, No. 3 (Sep. 1973), pp. 367–372.
3. John James, "Evidence for flying buttresses before 1180", in Journal of the Society of Architectural Historians, Vol. 51, No. 3 (Sep. 1992), pp. 261–287.
4. Prache, Anne, "Les Arcs - boutants au XIIe siècle", in Gesta, Vol. 15, No. 1 (1976), pp. 31–42.
5. Russ Rowlett, Canadian Flying Buttress Lighthouses, in The Lighthouse Directory.
6. Alex Lee, James Arndt, and Shane Goldmacher, Cathedral Architecture.
7. Mark, R. & Jonash, R.S., 'Wind Loads on Gothic Structures' in Journal of the Society of Architectural Historians, 29:3 (Oct. 1970), pp. 222–230.
8. A Dictionary of Architecture, James Stevens Curls, Editor. 1999:Oxford. p. 501.

References

•  Chisholm, Hugh, ed. (1911). "Flying buttress". Encyclopædia Britannica (11th ed.). Cambridge University Press.