Expediting Delivery with Fabric Buildings

Design and Construction

By Eric Donnay

In a constrained supply chain environment with rapid deployment needs, installations such as Naval Station Rota, Spain, have leveraged rigid-frame fabric buildings for their quicker lead time, flexible design, and durable construction.
Rigid-frame fabric buildings can provide installations with expedited delivery timelines, as well as the ability to provide precise clearances for aircraft hangars and other structures. Photos courtesy Legacy Building Solutions.

Recent years have offered an extended lesson in not taking anything for granted. Many preconceived notions of product accessibility and delivery timelines were turned upside down in the pandemic and its ripple effects through global supply chains. While certain items now can be secured somewhat quickly, supplies for new building construction have come with a longer lead time.

For many military building applications, long lead times are a non-starter. The conventional brick-and-mortar construction approach is required in certain instances, but in several others, rapid deployment is more critical. In many instances on military bases, getting the facility erected is the imperative. To meet the demanding timelines, engineers are more often turning to tension fabric buildings as a solution. A recent project at Naval Station Rota, Spain, underscores the timeline and operational benefits of this approach.

The U.S. Navy contracted with Legacy Building Solutions to build a pair of maintenance, repair, and overhaul hangars as part of an effort to stand up a new helicopter squadron in Europe. By constructing these hangars as fabric buildings, Naval Station Rota was able to meet its needs on an expedited schedule.

Solid Engineering

Fabric structures have a long track record of enabling expedited project delivery. Although permanent U.S. government building projects can take years for approval, tension fabric structures are often technically classified as temporary. This distinction helps expedite the entire process. Additionally, these buildings historically 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.

Epoxy paint can be used to protect the structural steel frame of fabric buildings when they are placed in a corrosive environment, such as near the ocean coast.

The ability to provide fast turnaround with a tension fabric building project has not changed, but the way these structures are built has evolved. Traditional fabric structures once consisted of a hollow tube, open web truss frame that is covered with a fabric roof. The problem with this approach was that there were too many engineering assumptions being made when designing and assessing the integrity of a web truss frame.

The solution adopted by manufacturers over the past decade to address this challenge has been to move away from design subjectivity and toward framing that was universally accepted and understood by the engineering community. Web truss began to be pushed aside in favor of a rigid-frame design that used structural steel I-beams. This is the design style utilized at Naval Station Rota. Following this new approach gave the installation’s new buildings a conventional look and a strong, durable design for permanent applications.

Accommodating Design

Rigid-frame engineering makes it possible for fabric buildings to move beyond standard sizes and allow for more configuration depending on site need. Every building now can be designed to the exact dimensions desired and required. The increased strength of the frame also allows for buildings to be made much taller and wider than before, expanding the possibilities of potential configurations. And because full designs are done using metal building software programs, there is little additional lead time to render a complete building frame.

I-beam design is also effective in combatting external loads from forces of nature like wind and snow. Depending on where in the world a base is located, rigid-frame fabric structures can be designed to withstand heavy snow loads and hurricane-level wind speeds.

At Naval Station Rota, each hangar measures 100-ft wide by 100-ft long in an optimized design. Of the two hangars, one features a bridge crane with 5-T capacity supported by the I-beam frame, while the other was engineered to be crane-ready if the need to add one arises in the future. The project team worked closely with the general contractor to customize a suitable foundation for the fabric structures that would accommodate the layout, particularly for the rolling door entrance to each hangar since the existing tarmac on the site was sloped for drainage.

Application Readiness

It is common for the structural steel frame of a fabric structure to remain exposed and visible within the building interior. For situations where the I-beams could be affected by corrosion (such as when situated near the ocean coast like Rota or when storing salt or other corrosive materials) users have traditionally utilized hot-dip galvanizing to treat the steel. However, galvanized zinc is only intended to delay corrosion, not stop it. Instead, at Rota, epoxy paint was employed in this project as an enhanced corrosion protection measure. This will create a true barrier between the steel and any corrosive elements present, allowing for many more years of longevity for the building frame.

I-beam design allows for strengthening the building frame only where necessary to accommodate hanging loads like overhead cranes, such as a 5-T crane used
at Naval Station Rota, Spain.

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 fabric is the typical choice for military structure roofing and sidewalls. In recent years, some offerings have been upgraded with additional coating layers, better ultraviolet inhibitors, and cold cracking resistance down to -40°-C. The expected longevity of these newer materials is almost twice that of fabrics previously available.

For applications like warehouse storage, fabric 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 summer and warmer conditions in winter.

Fast, Lasting Results

The designers and engineers charged with developing military buildings need to prioritize fast delivery within a budget, but this does not mean the end result has to be temporary and cheap.

Today’s fabric building engineering allows for the procurement 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. Rigid-frame fabric buildings also can be more airtight than comparable metal buildings, and their interior environment can be further controlled through the use of insulation and fabric liners.

Meeting Precise Needs

The precise dimensions made possible by the rigid-frame concept implemented in recent years makes it easier to meet code requirements while optimizing building design and limiting the need to invest in excess materials. For example, fabric structures are among the most common and cost-effective shelter choices for military aircraft. The code requirements for aircraft hangars are very strict, requiring 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. If a width of 85-ft was needed, a supplier would have to go to a 100-ft-wide option since the 80-ft offering would not suffice. This had the downside of adding 15-ft more than needed to the project footprint, which could cause additional issues. Using rigid-frame design, engineers now can provide the most optimal dimensions and avoid wasting space or money.

For applications where hanging loads are desired for implementing fire suppression systems, overhead cranes, or other 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 building load factors. This precision makes it simple to strengthen the frame only where necessary, rather than over-engineering the entire structure at a higher cost.

Eric Donnay is Vice President of Sales & Marketing, Legacy Building Solutions; edonnay@legacybuildingsolutions.com.

Article published in The Military Engineer, November-December 2024

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