An air-supported (or air-inflated) structure is any building that derives its structural integrity from the use of internal pressurized air to inflate a pliable material (i.e. structural fabric) envelope, so that air is the main support of the structure, and where access is via airlocks.
It is usually dome-shaped, since this shape creates the greatest volume for the least amount of material. To maintain structural integrity, the structure must be pressurized such that the internal pressure equals or exceeds any external pressure being applied to the structure (i.e. wind pressure). The structure does not have to be airtight to retain structural integrity—as long as the pressurization system that supplies internal pressure replaces any air leakage, the structure will remain stable. All access to the structure interior must be equipped with some form of airlock -- typically either two sets of parallel doors or a revolving door or both. Air-supported structures are secured by heavy weights on the ground, ground anchors, attached to a foundation, or a combination of these.
Among its many uses are: sports and recreation facilities, warehousing, temporary shelters, and radomes. The structure can be either wholly, partial, or roof-only air supported. A fully air-supported structure can be intended to be a temporary or semi-temporary facility or permanent, whereas a structure with only an air-supported roof can be built as a permanent building.
The biggest air-supported dome in North America is the dome at the École secondaire publique Louis-Riel (Louis-Riel Secondary Public School) in Ottawa, Ontario. It is the second biggest air-supported dome in the world.
The shape of an air-supported structure is limited by the need to have the whole envelope surface evenly pressurized. If this is not the case, the structure will be unevenly supported, creating wrinkles and stress points in the pliable envelope which in turn may cause it to fail.
In practice, any inflated surface involves a double curvature. Therefore the most common shapes for air-supported structures are hemispheres, ovals, and half cylinders.
The main loads acting against the air-supported envelope are internal air pressure, wind, or weight from snow build-up. To compensate against wind force and snow load, the structure's inflation is adjusted accordingly. Modern structures have computer controlled mechanical systems that monitor dynamic loads and automatically compensate the inflation for it. The better the quality of the structure, the higher forces and weight it can endure. The best quality structures can withstand winds up to 120 mph (190 km/h), and snow weight to 40 pounds per square yard.
The air pressure on the envelope is equal to the air pressure exerted on the inside ground, pushing the whole structure up. Therefore it needs to be securely anchored to the ground (or to the substructure in a roof-only design).
For wide span structures cables are required for anchoring and stabilization. Anchoring requires ballast (weights). Early anchoring designs incorporated sand bags, concrete blocks, bricks, or the like, typically placed around the perimeter on the seal skirt. Most modern design structures use proprietary anchoring systems.
The danger of sudden collapse is nearly negligible, because the structure will gradually deform or sag when subject to a heavy load or force (snow or wind). Only if these warning signs are ignored or not noticed, then the build-up of an extreme load may rupture the envelope, leading to a sudden deflation and collapse.
The materials used for air-supported structures are similar to those used in tensile structures, namely synthetic fabrics such as fibreglass and polyester. In order to prevent deterioration from moisture and ultraviolet radiation, these materials are coated with polymers such as PVC and Teflon.
Depending on use and location, the structure may have inner linings made of lighter materials for insulation or acoustics. Materials used in modern air supported structures are usually translucent, therefore the use of lighting system inside the structure is not required during the daytime.
The interior air pressure required for air-supported structures is not as much as most people expect and certainly not discernible when inside. The amount of pressure required is a function of the weight of the material - and the building systems suspended on it (lighting, ventilation, etc.) - and wind pressure. Yet it only amounts to a small fraction of atmospheric pressure. Internal pressure is commonly measured in inches of water, inAq, and varies fractionally from 0.3 inAq for minimal inflation to 3 inAq for maximum, with 1 inAq being a standard pressurization level for normal operating conditions. In terms of the more common pounds per square inch, 1 inAq equates to a mere 0.037 psi (2.54 mBar, 254 Pa).
Advantages and disadvantages
||This article contains a pro and con list, which is sometimes inappropriate. (November 2012)|
There are some advantages and disadvantages as compared to conventional buildings of similar size and application.
- Considerably lower initial cost than conventional buildings
- Lower operating costs due to simplicity of design (wholly air-supported structures only)
- Easy and quick to set up, dismantle, and relocate (wholly air-supported structures only)
- Unobstructed open interior space, since there is no need for columns
- Able to cover almost any project
- Custom fabric colors and sizes, including translucent fabric, allowing natural sunlight in
- Continuous operation of fans to maintain pressure, often requiring redundancy or emergency power supply.
- Dome collapses when pressure lost or fabric compromised
- Cannot reach the insulation values of hard-walled structures, increasing heating/cooling costs
- Limited load-carrying capacity
- Conventional buildings have longer lifespan
Notable air-supported domes
- Alaska Dome, Anchorage, Alaska
- Bennett Indoor Athletic Complex, Toms River, New Jersey, United States
- Carrier Dome, Syracuse, New York, United States
- Dalplex (athletics complex), Halifax, Nova Scotia, Canada
- Sports Complex Dome, Muncy, Pennsylvania, United States
- Harry Jerome Sports Center, Burnaby, British Columbia, Canada.
- Krenzler Field, Cleveland State University, Cleveland, Ohio, United States
- Tokyo Dome, Tokyo, Japan
- USF Sun Dome Tampa, Florida, United States
Former notable domes
- BC Place, Vancouver, British Columbia, Canada (formerly largest air-supported stadium in the world. The roof was changed to a retractable roof in 2011.)
- Burswood Dome, Perth, Western Australia (Demolition commenced June 2013)
- Dakota Dome, Vermillion, South Dakota, United States (air-supported roof was replaced by a steel frame domed roof in 2001)
- Hubert H. Humphrey Metrodome, Minneapolis, Minnesota, United States (Roof deflated January 18, 2014, to be demolished in February 2014)
- RCA Dome, Indianapolis, Indiana, United States (demolished in December 2008)
- Pontiac Silverdome, Pontiac, Michigan, United States (deflated in early January 2013; may possibly be renovated with new permanent roof)
- St. Louis Science Center Exploradome, St. Louis, Missouri, United States (Demolished in 2013)
- UNI-Dome, Cedar Falls, Iowa, United States (air-supported Teflon/Fiberglass roof was replaced with a steel frame-supported stainless steel/fiberglass roof in 1998.)
- "David Geiger, Engineer, 54, Dies". The New York Times. 1989-10-04.
- Yeadon Air Supported Structures (2005-03-15). "Yeadon's Most Recent Successful Project March 2005". Retrieved 2012-06-12.
- D.A. Lutes (May 1971). "CBD-137 Air-Supported Structures". National Research Council Canada. Archived from the original on 31 October 2009. Retrieved 2009-10-19.
- DUOL Air Supported Structures (2012-01-03). "DUOL air domes". Retrieved 2012-01-03.
- "Sports Complex Dome". www.visitpa.com. Retrieved July 20, 2014.
|Wikimedia Commons has media related to Inflatable buildings.|
- NRC Canadian Building Digest CBD-137 - 1971 Online version
- Tension Structures
- DESIGN MANUAL FOR GROUND-MOUNTED AIR-SUPPORTED STRUCTURES
- GUIDE FOR ESTIMATING MAXIMUM ANCHOR LCADS ON AIR-SUPPORTED STRUCTURES