The Types of Domical Steel Frames

Three-Hinged Truss

• The three-hinged truss consists of two parts, each acting as a single piece that depends on the opposing force of the other piece to keep it in position. Each part is a semi-braced arch where the upper and lower members connect to bracing to form a curved steel rafter. This type of domical frame often occurs in exposition buildings, armories and train sheds throughout the U.S.

Lamella Frame

• A lamella style frame consists of short steel members (lamellae) hinged together to form a crisscrossing pattern of skewed parallel arches. This diamond pattern of trusses exists in the Houston Astrodome and the New Orleans Superdome. The lamella style frame extends to three dimensions for form space trusses, such as that used in the Narita Hangar at Tokyo International Airport.

Dome

• The geodesic dome design, from the 1940s, includes metal ribs placed in a triangular or hexagonal pattern that lie on the great circles of a sphere, called geodesic lines. You can find an example of this design in steel at the Union Tank Car Company in Wood River, Illinois. Most commonly, this design utilizes aluminum, such as that found in the Poliedro de Caracas, in Venezuela. Shell vault is the term for this design when constructed from aluminum tubes.

Bow-String Arch

• As in the International Rail Terminal at Waterloo, the domed roof consists of bow-string arches pin jointed at the base. A third pin joint positioned to one side allows the structure to change form. Arches of this design are flatter than many other domed designs to reduce the volume of enclosed space. Tapered steel trusses with steel castings lighten the appearance of the structure. A variation of this design using cross arches exists at the Ponds Forge International Sports Center in the U.K..

Portal Frame

• In a portal frame design, standard beam sections bolt together with various joint types. The simplicity and efficiency of the portal frame system provides workable enclosures for manufacturing and storage facilities. You can see an example of this design at the Modern Art Glass Warehouse in Thamesmead, England, where the use of color greatly enhances its simplicity.