Flying buttress
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A flying buttress, or arc-boutant, is a specific type of buttress usually found on religious buildings, especially cathedrals. They are used to transmit the horizontal force of a vaulted ceiling through the walls and across an intervening space (which might be used for an aisle, chapel or cloister), to a counterweight outside the building. As a result, the buttress seemingly flies through the air, and hence is known as a "flying" buttress.
Although they are considered a hallmark of Gothic architecture, they were employed by the Byzantines, and in early Romanesque work, but were generally masked by other constructions or hidden under a roof. However, by 1150 flying buttresses were intentionally left exposed by architects and became decorative features in their own right, such as in the cathedrals of Chartres, Sens, Le Mans, Paris, Beauvais, and Reims.
Its presence outside the clerestory walls created a web of stonework that disguised the solidity of the structure, and gives the impression that the cathedral is being suspended from heaven. It balanced the network of ribs under the interior vaults that give the same impression, as if the upper stonework is forming a tent-like canopy over the congregation.
This technique has also been used by Canadian architect William P. Anderson to build lighthouses at the beginning of the 20th century.[1]
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[edit] Construction
"To build the flying buttress, it was first necessary to construct temporary wooden frames which are called centering. The centering would support the weight of the stones and help maintain the shape of the arch until the mortar was dry. 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."[2]
Because the majority of the load is transmitted from the ceiling through the upper part of the walls, making the buttress as a semi-arch extending far from the wall provides almost the same load bearing capacity as a traditional buttress engaged with the wall from top to bottom, yet in a much lighter and cheaper structure. And because the flying buttress relieves the load bearing walls with a much smaller area of contact, much larger voids are able to be built into those walls, such as for windows, than would otherwise be possible. Occasionally, due to the great height of the vaults, two semi-arches were used one above the other, and there are cases where thrust was transmitted through two or even three buttresses in a series. The vertical counterweight portion of flying buttress were often capped with pinnacles to give greater power of resistance.
[edit] Remedial
Another application of the flying buttress is to prop up a wall which may be leaning with a danger of collapse. An example is found at Chaddesley Corbett, where the wall of the south aisle of the parish church is leaning outwards. A flying buttress has been added as a more practical option instead of dismantling the wall and rebuilding it. The aisle was built in the 14th century, and dismantling it would be a major work. The accompanying picture also shows another form of buttress.
[edit] See also
[edit] References
- ^ Russ Rowlett, Canadian Flying Buttress Lighthouses, in The Lighthouse Directory.
- ^ Alex Lee, James Arndt, and Shane Goldmacher, Cathedral Architecture.
"Flying buttress". Encyclopædia Britannica (11th ed.). 1911.
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