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niranjana
niranjana • Mar 30, 2011

The Georgia Dome - The Fabric Roofed Architecture

The domes have been a part of the civilization for many years. There is one dome that I think is worth mentioning. It is the Georgia dome in USA. It has uniqueness to it. It is not made using full concrete or full steel. It is the world’s first large-scale oval dome. It is made using light weight fabrics and is made to stay stiff by using some tensegrity structures. Before I explain what exactly a tensegrity structure does let’s see the details of stadium having this dome.

Fact file:[​IMG]

Location: Atlanta, Georgia, USA

Completion Date: 1st march, 1992.

Cost: $214 million

Type: Cable-supported roof (tensegrity)

Purpose: Recreational (concerts, basketball, gymnastics, etc.)

Materials: Steel (8,300 tons), reinforced concrete (110,000 cubic yards), Teflon-coated Fiberglass

fabric roof design: Matthys Levy; Weidlinger Associates

Roof fabrication/installation Birdair Inc., Amherst, NY

Architects Heery/RFI/TVS, Atlanta, a consortium consisting of members from Heery International Inc., Rosser Fabrap International, and Thompson, Ventulett, Stainback & Associates; Scott Braley, AIA, project director

Seating: nearly 75,000

Diameter: 840 feet (the world’s biggest dome)

Height: 745.75 feet (227.30 m)

Floor area: 102,149.51 square feet

[​IMG]A tensegrity structure is one structure where the stiffness or support is given by the process of having stiff rods connected by prestressed cables. This pre-stressing allows the cables to take more tensile force than it can normally take. The loading members which are the rods are stiff and take only compression force and the cables take only tensile force.

So this action allows it to stay unsupported without the columns. This aspect has been made use of in this dome structure. If it is of a smaller span an option would be to have columns all around. But when we build a stadium that is to be covered there are two requirements.
  • It will have a large span.
  • It must have the unsupported roof at a great height so that it does not cause any hindrances to the people using it.
[​IMG]

The above picture will show the section through the major and minor axis of the dome. Here the vertical straight lines are the compression members which are the stiff rods. The inclined and the horizontal lines are the prestressed cables. In the centre line along the major axis alone there is a truss element 56m long connecting the two foci. These cables are connected to the rods with the help of bolts and welds. The whole structure makes the dome stay stiff.

The roofing material is Teflon coated fiber-glass fabric. A solid roof would be requiring less maintenance but for this kind of purposes the fabrics are most suitable as they can span larger length without any supports. The reason is they are very light. The fabrics are triangular in shape and connected to the adjacent triangles. The cables see to it that no tension is transmitted to the fabric and all the tension is carried by the cables alone.

It is this precise movement of pulling and pushing that allows tensegrity roof in the Georgia Dome to soar far above the stands and the playing field below.

Image Credits: Gadome | Columbia

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