Contractors building the Superdome also found that it required efforts and techniques that were a bit out of the ordinary, especially in the construction of its roof. For this building, the largest clear span steel structure in the world (as attested to by the new Guinness Book of World Records) is literally held together by its roof. In its flying - saucer-shaped design , the walls of the Superdome literally hang (for want of more descriptive term) from the roof, with the force vectors at foundation level pointing away from the center.
The uniqueness of the Superdome's roof, designed by Binkley Engineering Company of St. Louis (formerly Roof Structures, Incorporated) is its "lamella" configuration, which is nothing more than a series of overlapping triangles building out from a ring in the center. This gives stability against any downward forces. The Superdome's 75-ton, 124-foot-diameter (38 meters), gondola handing from the center of the roof, gives it a stability against upward forces as well.
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The entire Superdome was designed with the intention of making everything in it capable of contributing to the stability of the structure. Its superstructure has four main column lines as the perimeter of the building to support the building and the seat bents and meeting room spaces. The columns supporting the tension ring are on 22-foot (6.6 meters) centers, arranged in a perfect circle. The columns for support of the seat bents cantilevering 65 feet (21 meters) are set in two separate rows that make up the "Squircle" pattern (the interior of the building is slightly elliptical in shape). An outer row of columns frames the convention room area.
Wind bracing is placed between the seat bent columns and Superdome columns, alternating between the three rows of columns and places where it doesn't interfere with the concourses or lobbies.
The roof had to be analyzed separately because of its unique construction. First of all at the building's perimeter, K bracing extends out from the Dome columns to provide additional wind bracing and also to accommodate the rain gutters surrounding the Superdome' s 2,200 foot (660 meters) perimeter. The upper arms of the K's support the 96 sections of the gutter, each 22 feet (6.6 meters) long by 10 feet (3.1 meters) by 4 feet (1.25 meters) deep.
Atop the 96 Superdome supporting columns rests the tension ring on 4-inch diameter (10 centimeters) rocker bearings. The bearings allow movement of the entire ring due to temperature contraction and expansion of about 3 inches (7.7 centimeters) in either direction from the column center ring.
The 9-foot (2.8 meters) ring consists of top and bottom chords and diagonals of 14 inch wide (36 centimeters) flanges.
Principal framing of the roof consists of 12 main rings at 30 degree intervals spanning from the 5-foot (1.5 meters) crown block to the tension ring. The ribs are connected by five concentric interior rings about 56 feet (17 meters) apart. Secondary trusses fill in and span from the intersection of main ribs and interior rings to the perimeter tension ring.
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Topping the steel roof deck of the Superdome is an inch thick layer of polyurethane, and topping that is a thin layer of hypalon, which is a synthetic waterproof covering.
The hypalon is a Dupont product and technically the name for it is chlorosulfonated polyethylene. A good description of the material would be that it's "elastomeric," which means that it has the capability of elongating under a load and recovering quickly from release of that load, much like a carpet.
The hypalon covering, actually a liquid which has to be sprayed under pressure and then let dry because it is extremely sticky, was sprayed on the Superdome's roof under protection of special nylon bubbles (cocoons) which were erected to protect the spray from wind and the sun's ultra-violet rays as well. This entire roof covering procedure took 162 days. The cocoons were 110 feet (34 meters) wide by 200 feet (61 meters) long by 50 feet (16 meters) high. They were also used to apply the polyurethene.
Thanks for the roof info. Did the 10ft pillar that fell support anything? I mean main support.