A monolithic dome (from the Greek mono-, meaning "one," and -lithic, meaning "stone") is a structure cast in one piece over a form, usually of concrete or similar structural material. Dome Technology, in Idaho Falls, Idaho; South Industries, Inc., in Menan, Idaho; and the Monolithic Dome Institute (MDI), in Italy, Texas, are the primary sources of monolithic dome information and training.
Monolithic domes are a form of monolithic architecture.
History
The earliest form of monolithic dome structure could be considered to be the igloo. While it is constructed of blocks of compressed snow, these blocks melt and re-freeze to form a strong, homogeneous structure. The dome-like shape of the igloo exhibits the two major advantages of a dome-shaped structure: great strength and good insulation. The strength is due to the natural strength of the arch, and the insulation is due to the minimal surface area of a spherical section.
The first modern monolithic dome structure was built in Provo, Utah, and opened in 1963 as an ice skating rink. Called Ream's Turtle after its 1967 conversion into a general store by new owner Paul Ream, the building stood until it was demolished in 2006 for new construction.
Ream's Turtle was built by first creating a mound of dirt in the desired shape of the shell, an ellipsoidal section 240 ft (73 m) long, 160 ft (49 m) wide, and 40 ft (12 m) high. The mound was then covered in a grid of rebar, to provide strength, and a layer of concrete approximately 4 in. (100 mm) thick. After the concrete was cured, the dirt was excavated through the doorways, leaving the roof standing in its place. The floor was then poured to finish the structure.
Current Construction Methods
Modern construction differs significantly from the original concrete-over-dirt method. The current methods were developed by three brothers from Idaho— Barry, Randy, and David South. The first dome built using their methods was constructed in Shelley, Idaho.
- A rebar-reinforced concrete foundation is poured, defining the shape of the base of the structure.
- The fabric form, or airform, is attached to the foundation and inflated with an air blower. The airform contains an airlock to allow workers to enter the form while it is inflated.
- A 4 in. (102 mm) layer of polyurethane foam is sprayed inside the form. The foam serves several purposes: It will hold the rebar in place, provide support for spraying in the concrete mixture, and insulate the final structure.
- Rebar is attached to the inside foam by means of clips that are attached to the foam.
- Several inches of concrete are sprayed over the rebar frame. The concrete may be thicker at the bottom than at the top of the structure.
- After the concrete has set, the blower is turned off. The airform remains in place as an outer covering protecting the foam.
- The exposed surface of the airform may be covered with paint, stucco, wood shingles, stone, or almost any other type of surface treatment. Some type of covering is desirable to protect the airform from long-term degradation due to ultraviolet radiation.
- A non-insulated version of the monolithic dome is available in which the airform can be removed after completion and reused to build additional domes. MDI refers to this type of dome as an Ecoshell.
Durability
This domed government building in Baghdad, formerly a part of Saddam Hussein's regime, was hit by a 5,000 lb (2,300 kg) bomb. Apart from the hole made by the entry of the bomb, the building remained structurally sound.
The dome, when finished, is resistant to earthquakes, tornadoes, and hurricanes (FEMA rates the domes as "near-absolute protection" from F5 tornadoes and Category 5 Hurricanes). Recently, a number of monolithic domes constructed using MDI techniques have survived major disasters:
- Several monolithic domes in Florida survived direct hits by Hurricane Katrina.
- Several monolithic domes were in the path of the 2005 and 2006 wildfires in Oklahoma and Texas, and survived with only slight charring of the exterior foam insulation.
- In 2003, a monolithic dome mosque in Iraq survived a direct hit by a 5,000 lb (2,300 kg) bomb. The interior of the structure was totally destroyed, but the dome itself remained standing (see photo).
The demolition of Ream's Turtle also demonstrated the durability of the monolithic dome structure. A wrecking ball demolished a strip several feet wide around the perimeter of the structure, without a collapse. When a doorway on one side was pulled down, the dome finally tipped over, and collapsed.
Climate Control
The monolithic dome, for a number of reasons, is very energy efficient. The spherical sections of the dome offer minimal surface area for the volume they contain, so there is less surface for heat transfer with the outside air. The one-piece construction of the monolithic dome also eliminates many of the seams through which air can leak, though this advantage is mitigated to some degree in residential domes by the addition of multiple doors and windows. Because the insulating foam is placed on the outside of the concrete shell, the concrete acts as a heat sink inside the building, reducing interior temperature fluctuations far more than the traditional home's insulation inside a brick or stone veneer.
Disadvantages
While the monolithic dome has numerous demonstrated engineering advantages, there are also some disadvantages, both engineering and social.
Engineering
- The techniques used in monolithic dome construction are very different from normal construction methods, so only specially trained construction crews are suited for building a dome using the modern techniques.
- The spherical sections that are best suited to monolithic dome construction often result in oddly shaped rooms when divided up, which can result in wasted space in narrow corners. This effect can be minimized by constructing the dome on a stem wall, or by using an airform of such shape as to allow for straight, vertical walls at ground level.
- The monolithic dome's lack of seams may make it too well sealed; dehumidifiers are required in all but the driest climates.
Social
Social disadvantages of monolithic domes are to a large degree shared by geodesic domes, due to the similar shape and unorthodox construction.
- The radically different appearance of the domes decreases the appeal of their use as private residences—the standard circular base doesn't fit well on small lots found in many areas, and the strange appearance and design may run afoul of neighborhood building covenants. Depending on the situation, variations from the standard circular shape may be avaliable and can help alleviate some of these problems.
- Building permits may be difficult to obtain if local officials are not familiar with the monolithic dome.
- Resale of a monolithic dome home may be difficult because of its unconventional appearance.
Construction Records
The largest monolithic dome in the world is the home of Faith Chapel Christian Center in Birmingham, Alabama. It seizes the record at 72 ft (22 m) tall and 280 ft (85 m) in diameter. Inside is a floor area of 74,500 sq ft (6,920 m2) in two levels.
External Links
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "
Monolithic dome."
