• Steel is a more recent material used in construction of 3D compression systems. It is strong in both compression and tension. Steel can be used to form geodesic domes or radial arches rotated about a central axis. Unlike concrete, steel does not require formwork. Therefore, it can be prefabricated to save time. It can then be brought to the site and connected with welds and bolts as necessary. Because steel forms the skeleton of a dome, it allows for many windows to be inserted between the steel members. The steel structure can either be exposed to display the skeleton of the structure or simply used as the structural support. A steel dome can span up to 500ft and can reach heights up to 150ft. Steel is relatively heavy compared to concrete and brick, approximately 490 pounds per cubic foot.

• An advantage of steel is that it is very ductile, which makes it a better choice for areas that experience seismic activity. Another advantage is that it is less likely to experience total failure if one part of it fails because of its tensile strength. A disadvantage of steel, however, is that it is loses strength when exposed to high temperatures, such as in a fire, and may fail. In order to withstand the high temperatures longer and help ensure the safety of the occupants of the structure, the steel would have to be coated with spray-on fireproofing. Another disadvantage of steel is the high cost, about $160 per cubic foot (observed).

• Concrete is an ideal material for building traditional domes because it is very strong in compression and can be poured to any shape desired. Because of this, an attractive appearance can be achieved, making the structure the façade as well. Open areas of up to 250ft in diameter can be spanned with concrete domes, and heights of up to 70ft have been observed. Shell depths can be as thin as 2-3 inches, requiring a minimal amount of material. The weight of concrete is, on average, 145 pounds per cubic foot. This is almost a quarter of the weight of steel. Another advantage of concrete is that it is highly fire-resistant.

• While concrete can be used to make any shape imaginable and is a relatively inexpensive material to use for constructing 3D structures ($1.30-2.41 per sq. ft observed), a disadvantage is that the cost can steeply escalate when an irregular shape is required. Formwork is required to shape the concrete as it is poured. For regular dome shapes the same formwork can be reused. For irregular shapes, however, formwork needs to be made for the specific shape desired, resulting in increased costs.

• Plastic is a material not generally used in large scale building construction at this time. We think, however, that it may become useful in the future (possibly for bio-domes on other planets). Like concrete, plastic can be molded to fit any shape desired. Unlike concrete, however, it is very light (approximately 50-90 pounds per cubic foot). Like steel and wood, plastic can be used to form geodesic domes or radial arches rotated about a central axis and can be prefabricated to save time. Also like steel and wood, plastic has tensile strength as well as compressive strength which would result in less catastrophic failure.

• We expect that plastic domes would be able to achieve the same spans (up to 500ft) and heights (up to 150ft) as steel and wood and similar depths (as thin as 2-3in) as concrete. A disadvantage of plastic is that it is not very fire-resistant. Because plastic is not yet used as a major structural material yet, we haven’t found any codes governing fireproofing of this material. Another disadvantage is that plastic is sensitive to solar radiation. Over time, plastic would become brittle and both its compressive and tensile strengths would diminish.

• Wood, like all the other materials used for dome construction, is strong in compression. Like steel, wood can be used to form geodesic domes or radial arches rotated about a central axis and, therefore, does not require formwork. Wood domes can be assembled onsite or prefabricated to save time. Wood requires connections such as nails, screws, and bolts to hold the members together. Transporting the material to the site is easier because it is the lightest material used in dome construction, approximately 30 pounds per cubic foot. Wood domes can span areas up to 500ft and achieve heights up to 80ft. The depth of the wood can be anywhere from approximately 10in to 50in. An attractive wood can be used and the members left exposed or less expensive wood can be used to form the structural skeleton of the dome.

• We found prices of wood to range from $0.25-5.00 per square foot. Like steel, the wood also has some tensile strength which will make it less likely that the entire structure will collapse if one part of it fails. A disadvantage to wood, however, is that it is a highly combustible material and must be chemically treated to resist combustion during a fire. Another disadvantage, and a major difference between this and the other materials mentioned here, is that wood is subject to warping caused by temperature and moisture differences experienced in a particular area.

• Brick is the traditional material used throughout history for constructing 3D compressive structures because it embodies the essence of compression: one piece stacked on top of another. Although brick is not as strong in compression as concrete, it is sufficient to sustain the loads imposed upon it while weighing slightly less than concrete (approximately 120 pounds per cubic foot). Like concrete, brick can be both the structure of the dome and an attractive façade. Also like concrete, brick is highly fire-resistant. It is not a very good insulator, however.

• Through observation, we found that some brick domes are constructed as a double shell with a layer of air in between to serve as insulation. Unlike concrete, brick needs to be held together with mortar. Brick domes can span an area up to 250ft in diameter and can reach heights of up to 130ft (observed). The minimal allowable depth of a brick dome was found to be 8 inches. Brick costs about $2.19 per square foot.

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