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Air-supported structure

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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.

The concept was implemented on a large scale by David H. Geiger with the United States pavilion at Expo '70 in Osaka, Japan in 1970.[1]

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 largest air-supported dome in the world is currently being constructed in the Hudson Valley of New York State in the town of East Fishkill. Built by Air Structures American Technologies Inc. (ASATI), it is scheduled to open in September of 2017 and will be called The SportsKingDome. It will feature a 160 feet (49 m) high ceiling and 350,000 square feet (33,000 m2) of training space for athletics. The largest air-supported dome in the world was "The Dome" in Anchorage, Alaska at 180,000 square feet (17,000 m2) before being converted to a retractable roof in 2011.[2]

Design

Shape

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.[3]

In practice, any inflated surface involves a double curvature. Therefore, the most common shapes for air-supported structures are hemispheres, ovals, and half cylinders.

Structure

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[3] (21.7 kilograms per square metre.)

The interior of the Tokyo Dome exemplifies how large an area that can be spanned with an air-supported roof.

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.[citation needed]

Material

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.[4]

Air pressure

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).[3]

Advantages and disadvantages

Air-supported structures have advantages and disadvantages over conventional buildings of similar size and application:

Advantages:

  • Can be engineered to attach to a pre-existing structure[5]
  • 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)[6]
  • 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

Disadvantages:

  • 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 and cooling costs
  • Limited load-carrying capacity
  • Conventional buildings have longer lifespan

Notable air-supported domes

In operation

Former notable domes

References

  1. ^ "David Geiger, Engineer, 54, Dies". The New York Times. 1989-10-04.
  2. ^ The Dome (2016). "Learn All About The Dome". Retrieved 2016-05-20.
  3. ^ a b c 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. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
  4. ^ DUOL Air Supported Structures (2012-01-03). "DUOL air domes". Retrieved 2012-01-03.
  5. ^ "Wall and Building Attachments" Retrieved May 05, 2017
  6. ^ "Example Of Relocation Services Provided by: Arizon Building Systems" Retrieved May 05, 2017
  7. ^ "Sports Complex Dome". www.visitpa.com. Retrieved July 20, 2014.
  8. ^ "The Sun Dome". Retrieved 29 March 2015.
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