When most people think of fabric buildings they think of tents and pavilions—structures that serve important but ultimately temporary functions.
What they probably don’t imagine are structures that give pre-engineered metal buildings a run for their money.
The engineering behind a fabric building is nearly identical to its metal equivalent; the only major difference is that the former uses fabric cladding rather than metal.
The technology underlying fabric structures has evolved considerably over the last few decades, but many civil and structural engineers may be unaware of just how far they’ve come.
Fabric Structure Durability
“The fabric is a lot tougher than people realize,” said Ben Fox, president of Legacy Building Solutions. “From 12-ounce all the way up to 32-ounce and from polyethylene to PVC, there are a lot of different fabrics, and each has its own pros and cons.”
A natural question to ask of a fabric structure concerns its resistance to tearing. Will a careless employee with a box cutter sticking out of his pocket end up tearing a hole through the side of your building? Definitely not.
“It takes a lot of pressure to cut the fabric, so it’s not going to happen by accident,” said Fox. “It’s by nature a very tough material and very easy to repair if that’s needed.”
How do you repair a fabric structure?
The answer is probably what you’d expect: fabric welds using a combination of heat and pressure. Repairs range from adding a simple patch to replacing an entire section of the roof. However, that can be difficult if the cladding consists of a single piece of fabric. That’s where Legacy has an advantage:
“Our fabric is made in individual panels—typically 20 feet wide—and attached individually to the frame. One of the benefits of that is that the panels can be individually replaced. It’s a lot less inconvenient and costly for the customer.”
This panel design also helps fortify the roof cladding. Fox used the following scenario to illustrate:
“If you have a 100 ft by 100 ft building and just once piece of fabric covering the entire roof, then when there’s high suction from wind, the fabric will only be supported by each end frame. That’s when covers blow off.”
Although this might suggest that there are geographical limits to fabric buildings, that’s certainly not been the case for Legacy. The company has dealt with extreme snow loads in mountainous Chile and extreme wind loads on islands off the Western coast of Australia.
“Snow loads are never a really big challenge for us,” said Fox. “Wind loads become a big challenge once you get over 200 mph—at that point you have to do more reinforcing to the fabric—but that’s the same challenge the metal buildings face.”
Fabric Structure Longevity
Properly engineered and constructed, fabric cladding has a minimum life span of 20 years. The right coatings can push that into the 30-year range, but it’s more than just the material properties of the fabric that account for this already surprising lifespan.
“One of the keys to the longevity of the fabric cladding is to get proper tension on it in both directions: vertically and horizontally,” said Fox. “We call it biaxial tension. If the fabric’s properly tensioned, that’s when you get the longest lifespan.”
Fox described fabric structures in terms of three key aspects: the metal framing, the fabric and the attachment of the two. “You can have great engineering and great fabric, but if you don’t attach it properly it won’t last.” Fox added that the steel frame has a lifespan of 50 years or more, as is typical with other solid-framed buildings.
Legacy’s patented attachment system uses half-inch bolts to connect the keder rail to the top flange of the structure’s rigid frame. This allows the keder rail to slide horizontally on the top flange, thereby achieving horizontal tension in the fabric panels. This is a big part of what gives Legacy buildings their long lifetime.
Fabric Structure Size and Flexibility
The typical requested size for a Legacy fabric building ranges from 50 to 400 feet wide, depending on the building’s use and the snow load requirements in the area. Building length and height also vary based on the building application.
Although corrosive storage is the most common use for fabric buildings, other industries have started to take advantage of the benefits and customization fabric buildings offer.
“We’re doing a lot of recreation structures for indoor sports, like tennis and football,” said Fox. “We do a wide variety of industries: from aviation, where you need large spans with large doors, to casinos where you need a clean and fairly airtight environment.”
In fact, fabric structures tend to be more airtight than their pre-engineered metal counter-parts. “HVAC specialists are used to finding ten to fifteen percent air leakage in metal structures, but they only find one to four percent in ours,” said Fox.
The fabric’s translucency is also beneficial in daytime operations, since it cuts down on the necessary costs for lighting.
Perhaps the best evidence fabric structures’ flexibility comes from Legacy’s headquarters:
“Our office, our fabric plant and both steel plants are in fabric structures,” said Fox.
A key feature of fabric structures is their ease of erection.
“It’s simply a lot faster than a metal building, in delivery and especially installation,” said Fox. “It takes roughly half to a third of the man-hours needed to install a fabric structure versus a metal one. Once we’re contracted and the drawings have been approved, we’re able to deliver buildings in four to eight weeks, depending on the size of the structure.”
Once they’re erected, these structures can support overhead cranes, large conveyors and even mezzanines. Plumbing, HVAC systems and chimneys can be added to fabric structures, while also accommodating retrofits and reconfigurations.
“Extra openings, side walls and end walls: that’s very easy for us to do after the fact,” said Fox.
Does Fabric Beat Metal for Pre-Engineered Structures?
Fabric structures have come a long way in recent years. They offer virtually all the benefits of metal structures when it comes to durability, longevity and flexibility.
Not only that, but they can be erected faster and at a typically lower cost. “By the time you include construction, we’re the same price to 20-30 percent less than conventional [metal] structures,” said Fox.
For more information, visit the Legacy Building Solutions website.
Legacy Building Solutions has sponsored this post. It had no editorial input into this post. All opinions are mine. --James Anderton