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.
To build the 9.7 acre, 680-foot-diameter (205meters) clear span roof hanging (American Bridge Division of U.S. Steel Corporation was the contractor) required the use of 37 scaffolds in concentric circles, as well as mobile cranes.
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.
American Bridge Division's efforts were crowned on June 12, 1973, a time that was referred to as the "most dramatic phase" in the Superdome's construction. It got underway at 6 o'clock in the morning, and was considered completed at 3:20 p.m. that afternoon, the Superdome's 680-foot roof (210 meters), the largest steel dome in the world was in place standing without support.
But in the words of Thomas M. Sutter, resident manager for the Superdome's design team of architects and engineers, it wasn't quite that simple.
As he put it later, "We didn't know for sure whether the roof would stand on its own until that moment." There were two men on top of each of the 37 towers used, and on top of these towers were hugh jacks. One by one, the jacks were lowered, inch by inch, until at last there were none supporting the roof.
Much of the ribbed steel roof deck was raised from the ground by helicopter which often make modern builders wonder how they did it when the dome of St. Peter's in Rome was built. Of course, that took more than 150 years, whereas, the Superdome, begun on August 11, 1971, was opened on August 3, 1975.
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.
For those workers who must fix the stadium's field lighting and hoist TV gondola equipment, all of which are in the eight foot space between the roof and the top of the steel lamellas, there are four catwalks, each about three feet (.6 meters) wide, so that the workers can get close to the necessary fixtures.
For example, there are 520 smoke and heat detectors throughout the Superdome itself, along with 70 fire alarm stations and 32 switches to automatically report to a constantly monitored master control panel the occurrence of a fire to the locations of a sprinkler head or fire hose in use.
All meeting room areas and restaurants have sprinklers, and hydrants are also located around the stadium floor. The largest entrance gate at the South end allows the largest fire equipment to drive right on to the arena floor if necessary.
For further protection, the Superdome has a rather novel rooftop ventilation system, that also is designed to play a role in emergencies. Upon a signal from any unit in the smoke detector system, pressurized hatches in the roof pop open.
The air conditioning (or heating) will be turned off and huge fans will turn on to draw fresh air along the ramps and concourses into the stadium proper, at the same time, drawing 3 million cubic feet of air out through the roof.
Smoke would thus exit through the top of the building and spectators leaving the Superdome would have fresh air coming into their faces and know they are heading for safety. The fans will move the equivalent of a wall of air one block wide, ten feet high, and moving at 10 mph in this operation.
There are 354 lightning rods on the roof.
Two concealed fire hydrants are installed at field level to provide ample hose streams to quickly extinguish any fire that might occur.
A total of 157 fire hose stations are located throughout the Superdome. These are equipped with a connected one and a half inch hose, as well as a hand fire extinguisher. A total of three miles of hose are used in these fire stations, which are located in such a way that any point in the building can be reached with spray from 100' of hose, or less.
To provide pressure for the sprinkler system and other firefighting equipment, two diesel power pumps are unaffected by electical outage. Each is capable of pumping 1,500 gallons per minute, providing water at 125 pounds per square inch of pressure.
THANK YOU for your sensible assurance about the structure of the dome.
Nita! Husband says thanks so much for the information. Dragged Himself away from his worktable to read the description you found, and he is impressed with your research abilities!
He is impressed with the overall structure of the roof, and likes the way the "doughnut" ring at the top of the structure is held down by the weight of the scoreboards, etc....
Hopefully the engineers will post to this, and offer their opinions, as they are the true experts in analyzing this kind of information. The only point of weakness that DH can see is the possibility of the "hypalon" being blown off. If it did, then the insulation would be exposed, and possibly blown off, then the steel roof deck would be vulnerable.
But, remember, an architect is totally dependant on engineers, who are the real experts on structural stability... and some engineers are a whole lot better than others, as is true with architects...
thanks interesting info, but it doesn't convince me it will stand , pray it doea.