If you've ever been on the "moon jump" at the fair or slept on an air mattress, then you know that fabric filled with air can support hundreds of kilograms of weight. This same principle is used at the Hubert H. Humphrey Stadium, also called the Metrodome, in Minneapolis, Minnesota. The stadium is an air-supported structure. The structure is covered with 10 acres of teflon
-coated fabric. This flame-retardant coating on the outside is strong enough to protect the fabric from ultraviolet radiation
from the Sun, air pollution, acid rain and other sources of physical damage. The stadium has 20 electric air fans to maintain a positive air pressure inside the structure, although only three usually operate at one time. A computerized peumatic
system continually monitors the air pressure and engages extra 100-horsepower fans when the air pressure drops. These fans can blow air into the structure at about 100,000 cubic feet per minute. While positive air pressure keeps the Metrodome up, 26 cables are connected to the fabric to keep the entire structure in place. Full-sized, air-supported sports stadiums are no longer being built in the United States. Too many problems with wet snow conditions and inadequate heating systems have had architects reconsider the design of large fabric-enclosed structures. Cable-supported or tensile
structures are currently the preferred design for stadiums. But designers have found other extremely practical uses for air-supported structures. They are used for temporary buildings and small sports facilities. The most exciting design is for hazardous waste clean-up sites. The air-supported covers prevent the sites from emitting toxic material into the environment.
You can observe the effect that moving air has on inflatable materials. Discover how important changing conditions are on an inflated structure and how moving air can support it. Materials
- Small fan with high and low settings and a protective covering
- 5 five-gallon plastic trash bags
- Masking tape
- cloth tape measure
- Thumb tacks
- Paper 1. Tape the open end of the trash bag around the front of the fan. 2. Turn the fan on low. After the bag inflates, measure its widest part. Record your observations. 3. Turn the fan on high and measure the bag again. Record the new measurements. 4. Now turn the fan off and remove the bag. Using the thumb tack, poke a number of holes in the bag. Record the number of holes you made. Retape the bag to the fan in the same manner as before. 5. Turn the fan on low and measure the bag again. Turn the fan on high and measure once again. Record both observations. 6. Try adding more holes or larger holes to the bag. ALWAYS REMEMBER TO TURN THE FAN OFF COMPLETELY EACH TIME YOU REMOVE AND REPLACE THE BAG. DO NOT PUT YOUR FACE OR HEAD IN THE PLASTIC BAGS!