By Sharon Thatcher, Rural Builder magazine – A popular choice by municipalities for the storage of salt and similar materials is tension fabric. The reason simply comes down to the harsh interior environments that a good fabric can handle.
“In a corrosive environment like a salt storage facility, fabric is simply going to last a lot longer than metal,” says Ben Fox, President of Legacy Buildings Solutions. “Corrosion resistance is the key benefit for building users who are storing salt, fertilizer or other corrosive materials. Those materials have virtually no damaging effects on a quality polyethylene or PVC roof.”
The average lifespan of the fabric, Fox says, is 20 years or more.
While corrosion isn’t a problem, the damaging effects of the sun are, so any coatings used on the fabric are there to help prevent UV damage, not rust or corrosion.
Steel framing and hardware are handled with hot dip galvanizing or other coating options to protect the steel.
Where there is salt, there is typically ice and snow, so that means a building that can handle what Mother Nature throws at it. Although load requirements vary by project, Fox noted that Legacy has designed buildings for heavier snow loads. “We just have to modify the design to account for specific user requirements and local codes,” he says. “If heavier loads are required, we might have to narrow our bay spacing width between frames to help the fabric hold that load.”
There are other benefits to using fabric for corrosive material storage, notably natural daylighting and energy efficiency. “Fabric has up to 12-percent translucency to allow natural light to permeate a building and save on the need for artificial interior lighting and electricity,” says Fox. “Fabric roofs also naturally moderate the inside temperature to be warmer in the winter and cooler in the summer. Insulation can be added when needed to meet certain building codes.”
Fabric buildings also offer a lot of design flexibility, “particularly when using a structural steel rigid frame instead of a hollow tube, web truss frame,” Fox adds. “Being able to customize sidewall heights and peak heights allows a building to accommodate larger doors or even ancillary equipment like conveyors or fire suppression systems on the structure itself.”
Not surprisingly, proper tensioning and attaching of the fabric are important for assuring a well-built tension fabric structure. “Our fabric panels are typically applied in 20 foot wide sections, and those far outlast really large fabric covers,” Fox explains. “Smaller panels are much more manageable to work with, so you can ensure that the fabric is at the proper tension and securely attached. Large fabric panels tend to be less secure and will allow some movement of the roof, which can make them susceptible to damage or other problems.”
Legacy is accustomed to dealing with municipalities when it comes to storage buildings. “It is a big part of our business. We’ve done buildings for the Department of Transportations in Indiana, Minnesota and North Dakota, among others at different levels of government,” Fox explains.
“We appreciate working with municipalities. They typically provide clear specifications that demand the high level of quality we strive for, and that tends to eliminate building manufacturers that don’t meet the specifications. They also demand proven engineering and usually require engineering reviews to verify that they are receiving a truly engineered building. The only challenge is that it is typically a longer sales process, but ultimately it’s worth it to know that all manufacturers are being held accountable.”
One of the municipal storage projects erected by Legacy Building Solutions last year was a new bulk salt storage facility at the Tulsa Port of Catoosa for the Oklahoma Department of Transportation. The massive tension fabric structure provides 50,000 tons of storage capacity for roadway deicing salt, nearly doubling Oklahoma DOT’s available storage across the state.
“ODOT will distribute the salt stored at this new location to maintenance distribution sheds ahead of impending snow or ice events during the winter,” said Craig Swengle, P.E. and associate vice president for Dewberry Engineers Inc., the primary engineer/architect for public improvements at the Port of Catoosa. “Previously, salt was stored in the open and covered with tarps after being off-loaded from barges. The new building will protect the salt supply from being compromised by wind and precipitation.”
Measuring 203 feet wide x 400 feet long, the structure features 16-foot cast-in-place concrete walls and a rigid frame roof design that maximizes the usable interior space. To eliminate corrosion concerns, Legacy Building Solutions installed a PVC tension fabric roof with structural steel frame that peaks to a maximum height of 70 feet. All of the building’s steel, components and hardware are hot dip galvanized.
“Once the general contractor completed the footings and floors, Legacy installed the fabric building very quickly, in about two weeks,” said Swengle. “It was a very positive process with professional communication between Legacy and Dewberry throughout the project.”
The new salt storage building is primarily clad with tan fabric, while also incorporating a white skylight to allow sunlight to illuminate the structure’s interior. The building is ventilated with mesh eaves and is designed to withstand winds of 90 mph and hold snow loads of 20 pounds per square foot.
The Tulsa Port of Catoosa was strategically chosen as the site for the new facility because it allows ODOT to transport salt to the northern part of the state on a barge via inland waterway. This reduces material transportation costs for the taxpayers and provides an avenue to procure extra salt shipments when road deliveries aren’t feasible.