Structural Integrity Comparisons of Three Styles of Air Structures
The three styles of air structures portrayed on this site are typical of the structures available from various manufacturers. It is important to understand that each of the three are mechanically inflated, much the same as when you blow into a balloon, and as such can "pop" if over inflated. The measurement of the amount of internal pressure that each style of structure will allow is measured in inches of "water static pressure" (wsp). Each structure has gauges to inform the operator of the current wsp at any given time, and for safety reasons, to inform them when the maximum wsp has been reached.
To provide a better understanding of the reason why the higher the wsp can be raised in an air structure, the better the structure will be able to cope with high winds and snow loads, it is necessary to know the relationship between internal pressure in wsp and external pressures applied against the structure by snow loading and high winds. A wsp of 1.75 inches is equal to an approximate wind pressure against the structure of 80 mph. If the wsp cannot be safely increased to compensate for higher winds or snow loads, the structure is at risk of collapsing.
1. The Cableless Dome or "Air Bag"
The cableless dome or "air bag", is only capable of a maximum of 1.5-1.6 wsp which will provide maximum stability against 60-75 mph winds and a snow load of 5-6 lbs. Little more than 1/2 a 10 lb bag of potatoes.
2. The "Hoop Cable Air Bag"
The "hoop cable air bag" is basically the same as the simple "air bag" except with steel cables spaced 8' to 21' apart crossing over the dome (and sometimes a few cables lengthwise), but this only provides the ability for a very small increase in inflation pressure of 1.75 to 1.8 wsp. The cables will provide a little more stability against higher winds (75-85 mph) and 5-8 lbs. Snow Load. The "hoop cable air bag" is still limited to a very small increase in the internal pressurization due to the stress that would be placed on the fabric and fabric seams should the internal pressure be raised beyond the safe wsp range. If you notice in the picture below of the Hoop Cabled Air Bag, the corners have no cables, and therefore the wsp cannot be raised.
Thermal skylight snowmelt is also required (no insulation in roof area) to assist in melting snow. Not having an insulated roof area will certaimly increase your annual heating costs due to exessive heat losses.
3. The Steel Bias Harness Net Structure
Finally a true Air Structure. The "Steel Bias Harness Net Air Structure" has the the highest structural integrity in the industry. Due to proprietary patents, the Steel Bias Harness Net System makes this unique structure the only Air Structure in the industry which can meet local building codes for permanent buildings.
Tennis Universal does not quote standards for tents, we quote standards for permanent buildings. We are offering an air structure so unique that it will meet your local building codes for permanent buildings. How do we offer so much more than any other company? It's simple. Tennis Universal researched all the known air structure companies, and found that only one company owned the patented technology capable of designing an air structure that met the standards we required.
The structure has a patented bias cable safety net system which totally surrounds the structure (similar to a hair net), which is attached to the anchorage system, reducing loads on the fabric providing optimum safety and stability in high winds, extending the life of the structure. The bias harness net system can be designed to allow the internal inflation pressures of 1.5-3.0 wsp, winds to 150 mph, and snow loads from 20-50 lbs. per square foot, depending on the geographical location requirements.
We encourage potential air structure customers to call their local building codes department to obtain the roof load and wind load specifications for permanent buildings in their geographical area. Why would anyone make a twenty year investment on a seasonal temporary structure that meets standards for tents, when they can have a seasonal temporary structure that will meet local building codes for permanent buildings.
Something To Think About When Researching Air Structures
If a staff member had to ascend to the top of an "Air Bag" or "Cable Air Bag" to remove excessive amounts of snow (which is necessary at times with the "air bag" and/or "hoop cable air bag"), the staff member's body weight alone could surpass the fabric's maximum load bearing design of 5-8 lb. per square foot. Truly a recipe for an avoidable accident.