Vaults

Example of a vault

Description

Vaults are generated by the projection of the arch section on a plan, which is most of the time horizontal. A vault is an arch-shaped structure, usually of masonry, used as the ceiling of a room or other enclosed space, as the roof of a building, or as the support for a ceiling or roof. Masonry vaults are often composed of voussoirs, which are held in place, like the stones of an arch, by the pressure of the neighboring pieces. A temporary supporting structure must be erected within the vaulted area during construction, because a masonry vault does not become self-supporting until the central voussoirs or keystones are put in place. A number of different types of vaults are used architecturally. The simplest of these is the barrel, or tunnel vault, the roof of which is shaped like half a cylinder and is supported by straight walls. A groined vault is formed by the intersection of two vaults of the barrel type, usually at right angles to each other. The junctures at which the two vaults meet are elliptical ridges, called groins. A dome can be thought of as an arch which has been rotated around its vertical axis. As such, domes have a great deal of structural strength. A small dome can be constructed of ordinary masonry, held together by friction and compressive forces.

Details and experiences

Building vaults

Building a vault with the Nubian technique

The back wall should be built first. It can have exactly the shape of the extrados of the vault or it can be quadrangular and the extrados of the vault will be drawn onto it. A template is needed to ensure the shape of the vault. It can advantageously be the future window frame on which are temporarily fixed some spacers to get the extrados shape of the vault. The template can also be made of welded Tor steel, which can be re-used afterwards for reinforced cement concrete.

It is necessary to create a net of string lines between the back wall and the template. Note that it is better to lay the net of string lines outside in the masonry. The reason is that any mistake in accuracy, with a block laid lower or slipping down, will not change the linearity of the string line.

In certain cases, it is sometimes necessary to lay the string lines below the masonry. It is then indispensable to work with a very high accuracy and to leave always 1 mm gap between the blocks and the string line.

Building a vault with the free spanning technique

We saw that this technique allows one to the lay courses horizontally and that it also uses vertical ones, like in the Nubian technique. What is presented here is only the particular details for laying the courses horizontally.

The binder varies when the vault rises. It starts with the same specification as for arches and progressively become more clayey. It is essential to check the balance of the portion of the vault which progressively corbels. Therefore, to ensure the height of the various courses their cord and span must be checked, to see if they are according to the calculations.

It is essential to compress the vertical joint very well and to keep it to the minimum, so as to reduce the shrinkage of the glue and cracks in the vault later on.

Acoustic of vaulted structures

Vaulted structures are characterised by two acoustic phenomena: echo and reverberation. Echo is a disturbing phenomenon which happens only in domes which are generated by the portion of a sphere. The dome might be built on a circular plan or on a quadrangular one (i.e. dome on pendentives) but it will always have an echo if it has the shape of the portion of a sphere or a shape close to the portion of a sphere. Hemispherical domes have the strongest echo. Pointed domes have rarely any echo but they can have a high reverberation and/or amplify the sounds. Domes which are generated by the intersection of vaults (i.e. cloister or groined dome) don’t have any echo at all.

Vaults and domes always manifest a high reverberation, which represents the time needed for the sound to fade away. This reverberation is due to 2 factors:

1. The size of the volume created by the vaulted structure, which is generally larger than other ones.
2. The shape of the structure, which tends to hold the sound within itself.

Echo and reverberation can be limited by acoustic correctors. These correctors are called single resonator absorbers. A German engineer, Helmholtz, elaborated some formulas to calculate them. The human voice ranges from 100 Hz to 2 kHz, with an average frequency at 400Hz. Correctors of various sizes can be installed to absorb the desired frequencies.

Composite Roofing with Brick Dome and Brick Vault

Description

The roofing structure here is a composite work of vaults and domes. The Domes are used for the main enclosures. The beam on which it rests cantilevers the slab outward. This is done for rain water drainage for which a gutter is provided along the edge of the slab.

Materials

• Brick
• Concrete
• China Mosaic

Details and experiences

Below is a wall section of the dome enclosure. Steel glass louvers from plinth level extend up to lintel level. Two reinforced concrete beams between which is a fixed glass opening.

Where in Auroville??

Yantra

Vaulted Roofing with Steel

Example of vault with steel

Description

The building is a vaulted structure with its principle material being steel. The Vault rest on steel columns on its sides and further supported near the middle on either sides over steel columns which rest on rammed earth walls. Box steel section columns are welded to ‘I’ section beams that run across the vault. Over this re steel and wooden purlins upon which an aluminum sheet is used.

Materials

• Steel Sections
• Wooden Purlins
• Aluminum Clad Sheet

Details and experiences

Where in Auroville??

American Pavilion

Links

Earth Institute earth institute

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