Using proven I-beam designs, fabric buildings can be fully optimized for any facility application
By Eric Donnay
The primary benefits of tension fabric buildings have been clear for decades: Fabric cladding doesn’t corrode, making it a great option for high-humidity facilities or corrosive material storage. In many applications, the cladding also allows for natural daylighting. The structures are cost-effective, and they go up fast.
Some of the downfalls have also been obvious: For a long time, buildings were only offered in pre-engineered designs with standard sizes to pick from. And depending on the manufacturer and materials used, longevity wasn’t always what was hoped for.
In recent years, however, leading manufacturers have made strides to eliminate the historic weaknesses of fabric structures, while maintaining and even enhancing their strengths. Better engineering has helped solidify fabric’s place as an ideal facility solution in a wide range of industries.
Fabric structure projects have a long history of short lead times. For decades, the main reason for this was that these buildings mainly only came in standard size offerings, meaning that very little thought had to go into the design. Typically, a pre-engineered size was selected “off the shelf,” and the structure was quickly installed in a matter of weeks or months.
The ability to provide fast turnaround with a tension fabric building hasn’t changed, but the way these structures are built has evolved for the better. The traditional fabric structure consisted of a hollow-tube, open web truss frame covered with a fabric roof. The problem was that there were far too many engineering assumptions being made when designing and assessing the integrity of a web truss frame. Disagreement from one engineer to the next was commonplace.
The logical solution over the past decade was to move away from design subjectivity and toward framing that was universally accepted and understood by everyone in the engineering community. Web trusses began to be pushed aside in favor of a rigid-frame design using structural steel I-beams. Legacy Building Solutions was the first company to marry together an I-beam frame with a tension fabric membrane.
In addition to being a proven method, rigid-frame engineering instantly made it possible to move beyond standard sizes and instead design every building to the exact dimensions desired. The increased strength of the frame allows for buildings to be made much taller and wider than before as well, making it perfect when long, clear spans without support beams are needed. Furthermore, because full designs are done using metal building software programs, there is virtually no additional lead time involved to render a complete building frame.
Some manufacturers, including Legacy, have gone a step further and handle their own in-house steel fabrication. By not outsourcing this key component of a fabric building, these companies are better positioned to ensure quality control, adapt to any project modifications, and eventually provide on-time delivery of the structure.
Codes and User Demands
The precise dimensions made possible by the rigid-frame concept make it far easier to meet code requirements while also optimizing the building design, helping to achieve all necessary considerations without investing in excess materials.
For example, tension fabric structures are among the most common and cost-effective shelter choices for aircraft hangars. The code requirements in the aviation industry are very strict, necessitating that there is always enough vertical and horizontal clearance around the wingtips of the aircraft in relation to the roof, door frames, or sidewalls of the building.
In the days of standard size fabric buildings, meeting these clearances mostly involved the manufacturer just taking the aircraft measurements and offering the smallest pre-engineered structure in their inventory that could achieve compliance. In other words, if a width of 85 feet was needed, a supplier would have to go to a 100-foot-wide option since their 80-foot offering wouldn’t suffice, which added 15 more feet than needed to the project footprint.
Using rigid-frame design, engineers can provide the most optimal dimensions and avoid wasting money or space that might be needed for future considerations. Dimensions, however, are far from the only parameter that can be optimized in a fabric building.
For applications where hanging loads are desired for implementing fire suppression systems, catwalks, overhead cranes, mezzanines, or other significant and heavy features on the frames, those loads can be factored into the original rendering. Using finite element analysis, the size and thickness of each individual beam can be manufactured to match the building’s load factors. This precision makes it simple to strengthen the frame exactly – and only – where necessary, rather than over-engineering an entire structure at a higher cost.
I-beam design is also tailor-made to combat external loads from forces of nature like wind and snow. Engineers can slope the roof and shape the sidewalls as necessary to withstand heavy snow loads, not to mention add ice breakers, gutters or other external roof features. For areas frequented by hurricane activity, buildings can be designed with wind ratings up to 240 miles per hour.
Internal Use Factors
It’s common for the structural steel frame of a fabric structure to remain exposed and visible within the building interior. Applications such as wastewater treatment, composting, fertilizer housing, and salt storage all create the added challenge of needing to protect the building frame from the damaging effects of corrosion.
When web truss was the industry standard, it wasn’t even possible to always know if the frame had been compromised. The hollow-tube frames could corrode from the inside out for a long time out of sight, potentially weakening the structure behind the scenes.
I-beam structures don’t experience that issue, of course, but are still vulnerable without proper treatment. Users have traditionally utilized hot-dip galvanizing to treat the steel.
However, recognizing that the galvanized zinc is only intended to delay corrosion and not stop it, some companies have turned to epoxy paint as an enhanced corrosion protection measure. Epoxy coating creates a true barrier between the steel and any corrosive elements present, allowing for many more years of longevity for the building frame.
Unlike a metal roof, fabric cladding itself is not susceptible to corrosion, but it still must contend with weather and other influences over time. Polyvinyl chloride (PVC) fabric has been the preferred choice for durable roofing and sidewalls. In recent years, some PVC offerings have been upgraded with additional coating layers, better UV inhibitors, and cold cracking resistance down to -40 degrees Celsius. The expected longevity of the newer PVC is almost twice that of fabrics previously available.
For applications like warehouse storage, fabric’s translucency allows users to take advantage of the natural daylight that permeates the roof, cutting down on the number of artificial lights needed inside. Fabric also moderates how outdoor temperature extremes feel inside the building, providing a cooler environment in the summer and warmer conditions in the winter.
Rigid-frame fabric buildings are more airtight than comparable metal buildings, and the interior environment can be further controlled through the use of insulation and fabric liners. Insulated fabric structures provide an ideal atmosphere for athletic and recreational facilities, where the fabric provides a soft reflective quality that lightens up the building and dampens echoes, contributing to a perfect ambience for sports and spectating.
The process of installing a fabric building is also far more efficient than conventional brick-and-mortar construction. Aside from using materials that can be erected faster, some fabric structure suppliers can further expedite the process by handling every aspect of a project in-house.
By employing their own design engineers, manufacturing I-beams and fabric panels in on-site facilities, and using their own professional installation crews – rather than relying on outside vendors for any of those steps – these companies can better stay on schedule, while also ensuring quality control for every component they touch.
Today’s fabric building engineering, in combination with improved materials and processes, has allowed for the development of facilities that are cost-effective, custom-designed to the exact needs of the application, and of a much higher quality and longevity than the tension fabric structures of the past.
Eric Donnay is General Manager, Legacy Building Solutions