Engineers help to ensure the practicality,
safety and success of fabric structures.
By Janice Kleinschmidt
In May, consulting architect Nicholas Goldsmith, FAIA, received a call for help with a tent for the July 4 Coney Island Festival and Flea Market. “A client who purchased a rental tent system from China set it up not realizing that the engineering used in China really wouldn’t apply to New York,” says the senior principal of FTL Design Engineering Studio in New York City. “After he set it up, the building department said he needed a local engineer to stamp the project. He brought us in, and we had to then do forensic engineering. We had to measure all the pieces. There were no drawings.”
A computer analysis confirmed that the structure would not meet local codes. “We had to come up with a design that would keep as much of the existing structure but had more framing to withstand wind,” Goldsmith says. Using its contacts with manufacturers, FTL was able to have steel reinforcements made, shipped and installed by the end of June.
“The cost was a lot more than if [the client] had just come to an engineer at the beginning and had them review products out there to select something that would meet the wind load,” Goldsmith says.
Respect the knowledge of all parties
As with any professional relationship, manufacturers and end-product users need to “respect the knowledge,” says Beth Hungiville, manager of the Fabric Structures Association (FSA, formerly Lightweight Structures Association), a division of the Industrial Fabrics Association International. “The key factor is to bring them in at the beginning so you don’t have issues at the end.”
Some projects—i.e., geosynthetic liners for waste containment, multipeaked canopies over theater seating, even temporary structures in potentially windy conditions—obviously need the expertise of engineers trained to perform load analyses and determine necessary framework. However, there are those who question the need for engineers in fabric applications.
“The whole purpose of engineering is not simply to satisfy public safety,” says Christopher Walker, senior vice president of international marketing for B & C Awnings Inc., Anaheim, Calif. “The legislative requirement by local authorities for engineering is also to generate permit revenue, control development, satisfy extra protection of insurance companies, who have lobbied for legislation to have it made a necessity.” Walker believes awnings are architectural and decorative features and only rarely a structural component or product.
“If our company were to approach an outside engineer to design,” he says, “this inexperienced engineer will over-design the project. It would no longer be cost effective or marketable because the majority of engineers today have little or no fabrication cost experience and will design an overkill that is totally outrageous in costs. We are constantly approached to re-design architecturally engineered projects to reduce costs which exceed budget.”
Consulting engineer Craig Huntington, president of Huntington Design Associates Inc. of Oakland, Calif., offers a rebuttal. “They probably have been lucky so far,” he says, noting that people who don’t use engineers “may get away with that approach 10 times out of 10 or 50 times out of 50, but we look to have designs that work all the time. That’s our job as engineers.” While an awning manufacturer may claim its products are not structural, “the [property] owner wouldn’t feel that way if there was a collapse of an awning … or possibly a life-safety hazard.”
Bring in a fabric specialist engineer
“A lot of engineering gets done through contractors,” Huntington says. Often his first contact with a project is when he receives a plan and elevation prepared by an architect who forwards them to the general contractor, who forwards them to a fabric contractor, who forwards them to Huntington. “I think the process gets subverted a lot of the time because architects are putting out designs where the fabric shape is not practical or economical in fabric. In all but the simplest structures with uncurved fabric, you need a fabric specialist engineer.”
He agrees that engineering is important at the start of the project. “It’s not just something you can cram at the end of the game after the shape has been made. There are a couple of reasons you need a specialist,” Huntington says. “One relates to the way we shape and analyze fabric structures and, in the end, the way the fabric membrane itself is patterned. That’s all done with very specialized software, which is expensive to acquire and takes a good deal of experience to know how to use. … Usual construction materials—wood, steel and concrete—are very adaptable in how they carry load. … Fabric, string, cable—all you can do is pull on it. All it resists is tension. Because of that, the way the shapes are derived is very different.”
Hungiville agrees that fabric expertise is critical “because the environment affects fabric differently than it affects other building materials.”
“Fabric structures are very particular. The programs that are used for doing engineering analysis are written for this industry and are fairly unique,” Goldsmith says. “I have been in situations where a client has had other engineers aboard and then realized they don’t understand the tent structure, and then we are called in to do it.”
“We use structural engineers all the time,” says Martin Brown, director of engineering for FabriTec Structures of Costa Mesa, Calif., which has five professional engineers on staff, plus a dozen designers and architectural experts. “They definitely have to be experts within the fabric industry.”
Weigh the benefits of on-staff engineers
FabriTec primarily uses its in-house engineers to help bring in projects and work with architects in the early stages of a design. “Once we have a contract, we probably use consultants over 50 percent of the time,” says Brown, who wrote specialty software licensed by the company’s consultants around the world.
Tentnology of Surrey, British Columbia, Canada, maintains six mechanical and structural engineers on staff. “We have developed our own proprietary software for fabric structure design and analysis,” says Suzanne Warner, who co-owns the company with her husband, professional engineer Gery Warner. “We do all of our own in-house engineering.”
Tentnology’s engineers perform specific tasks, be it concept, design, analysis, bills of materials, manufacturing or working with customers and authorities. “It’s a very expensive process to keep people—well-paid engineers—on staff,” Suzanne Warner says, “but you have got full control of the process, and we are much more responsive and reactive to the market needs because of that.”
Approximately ten percent of Fabric Structures Association members employ licensed engineers. “If you manufacture a significant number of structures, having someone on staff would be more advantageous,” Hungiville says, adding that they also are more familiar with the company’s product and operations. “If you do two or three structures a year, you are probably better off paying a contract engineer.”
“I would love to have an engineer on staff, but we don’t have enough of that kind of work to warrant a full-time engineer,” says Jim Richman, president of Academy Awning in Commerce, Calif. “We work with two or three engineers we use on a regular basis.
“We give [the engineer] a basic design based on our experience, saying we think we should use these members and these members based on other jobs that we have done that are similar. The engineer may say, ‘You need to make this stronger.’ We quote [a project price] based on the engineer’s recommendations. When we secure a job, we go back to them and have them fully engineer it.”
Academy typically takes over the project from there. But, Richman notes, “If we take the engineering to the city or county and they have questions, we could be going back and forth. We do project management ourselves. By the time we get permits, the engineering issues have been worked out.”
Huntington frequently runs into situations where he has not been brought into the picture at the appropriate time. “We will get a design that’s not well thought out. I will try to back up the process: ‘Let me talk to the architect and try to find out what he’s trying to do, whether he’s flexible, whether there are adjustments I can make. If not, we can make almost anything work in the end, but it may be very heavy, and it may be uneconomical.’ The problems we are seeing most often are inadequate slope and inadequate curvature.
“The problem is an economic one,” he continues. “It may be a few hours of time is all [that is needed] to create a responsible shape, to develop a performance specification. Even just a few hours of time put into that can save of lot of problems down the road.”
Speak the engineer’s language
Just about every geosynthetic project needs a professional engineer’s stamp, says Boyd Ramsey, vice president of technical business development for GSE Lining Technology Inc. of Houston, Texas. “It’s not really our choice [to select engineers]. They are selected by the property owners, site developers, city or municipal building departments.”
GSE employs six civil engineers, who interface with consulting engineers. They “talk to engineers in the language they are expecting to hear,” Ramsey says. “They don’t do design. I don’t want them doing design. What I want them to do is provide information to people who are doing the designs. Depending on the design, there’s a fairly rigorous list of things people need to know about our products. Engineers just love to have data, data, data, data.”
“We tell them what to do. It’s not the other way around,” Walker says. “We generate drawings and it’s up to the engineer to calculate the necessary, applicable materials to make that work. If an individual wants his project to be cost effective, he doesn’t want to build in too many bells and whistles for a factory to build it for him.”
“I think relationships are based on trust, and that certainly is one of the factors of a relationship between a professional and a company,” Goldsmith says. “Sometimes a professional is going to tell an owner something he may not want to hear, like the structure isn’t working for this [application]. I think that trust is an important part of it. I think it’s important for the owner to feel like his consultants are really on his side and will help him find solutions to his problems and be part of his team. At the same time, the engineer is going to have to balance that with something that’s safe and well built.”