Monolithic dome
From Wikipedia, the free encyclopedia
A monolithic dome (from Greek mono- and -lithic, meaning "one 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, in Italy, Texas, are the primary sources of monolithic dome information and training.
Monolithic domes are a form of monolithic architecture.
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[edit] 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 feet long, 160 feet wide and 40 feet high. The mound was then covered in a grid of rebar, to provide strength, and a layer of concrete approximately 4 inches 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.
[edit] 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 these method 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 four inch 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 it will insulate the final structure.
- Rebar is attached to the inside foam, using 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 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 re-used to build additional domes. MDI refers to this type of dome as an Ecoshell.
[edit] Durability
The dome, when finished, is earthquake, tornado and hurricane resistant (FEMA rates them 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 5000 lb. bomb. The interior of the structure was totally destroyed, but the dome itself remained standing (see picture).
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.
[edit] 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 is mitigated to some degree in residential domes by the addition of multiple doors and windows. By placing the insulating foam 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 of a brick or stone veneer.
[edit] Disadvantages
While the monolithic dome has numerous demonstrated engineering advantages, there are also some disadvantages, both engineering and social. Engineering disadvantages are:
- 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 disadvantages of monolithic domes are to a large degree shared by geodesic domes, due to the similar shape and unorthodox construction. These disadvantages are:
- The radically different appearance of the domes also decreases the appeal for 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, a large variety of variations available from the standard circular shape can avoid 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.
[edit] References
- Building Monolithic Domes, by Sean Lanham, Architecture Week
