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Positively portable structures

Exteriors, Features | September 1, 2013 | By:

Transportable fabric structures have been around for millennia—what makes today’s structures unique and practical are the high-performance characteristics of their cladding.

Native Americans have known for eons about the virtues of lightweight, flexible fabric-wrapped structures, long before Europeans arrived in North America in the 15th century. Camping enthusiasts have appreciated lightweight, portable tents for many generations. Likewise traveling rock concert road shows have benefited from the sophisticated techniques of mobile stages and performance-enhanced band shells. What all of these portable structures share is the use of fabric and its superior capability to provide economical shelter while contributing to an efficiency unmatched by more rigid materials.

Portable structures have advantages that permanent structures do not, especially for activities that are intermittent or short-term in nature like musical and theatrical performances or social events such as political rallies where the use of a facility is one-off or short term. These types of structures can take many forms and use any manner of materials, but, logically, lightweight materials, such as high-performance fabrics or composites, can provide advantages and have a significant impact on the deployability, overall weight and success of a structure.

The most common designs incorporate a combination of rigid elements, or struts, with flexible fabric membranes that enclose. Some designs are completely made out of fabric and incorporate air beams for structure and erect on site using pumps or fans, relying on a cushion of air to support both structure and cladding.

Three basic types

According to Robert Kronenburg, in his book Architecture in Motion, there are three types of portable structures: portable buildings, deployable buildings and demountable buildings. “The idea that architecture can be portable,” Kronenburg says, “is one that grabs the imagination of both designers and the people who use it, perhaps because it so often forecasts a dynamic and imaginative solution to the complex problems of our contemporary mobile society.” At the same time, he maintains, these dynamic solutions deal with issues of practicality, economy and sustainability.

Nicholas Goldsmith, FAIA, LEED AP, senior design principal of FTL Design Engineering Studio, who has designed many transportable structures, further defines Kronenburg’s three types of structures: “Portable buildings can be structures that are transported whole and intact. These have limited use due to transportation restrictions on road and rail. Deployable buildings can be transported in sections and assembled on site. These are almost always carried to site by vehicles, but in a few cases may have part of their transportation system incorporated into their structure. The main advantage of this type of structure is that it can provide space almost as quickly as the portable building without the restriction in size imposed by transportation.”

Demountable buildings, according to Goldsmith, are composed of many smaller parts that are assembled on site. These types “are much more flexible in size and layout,” he says, “and can usually be transported in a relatively compact space. In short, demountable buildings are really designed as prefabricated ‘erector set’ kits.” All of these types of portable buildings can benefit from the use of fabric’s light weight and low embodied energy.

The fastest deployable facilities FTL has created are used for military operations. “The LANMAS and TME facilities,” Goldsmith says, “are air tube supported structures that use a patterned tensile fabric membrane as lateral support to create a truly synergetic structure with both elements dependent on each other. LANMAS uses a low-pressure air system, and TME uses a medium pressure system (30 psi) with exotic compound fabrics.” Both can be erected in less than one hour after initial layout and staking. These systems are used as shelters for helicopters and officers quarters in Desert Storm type applications. What is different with these designs from traditional air tube structures is that no constant air pressure is required once the arches are inflated.

The air, apparent

“Portable, architectural air structures have very few limitations,” says Ron Howell, director of Inflate USA, a subsidiary of the UK-based parent company Inflate GB. “As far as placement within a venue, fabric air structures can be deployed in a wide variety of environments—grass, sand, concrete or asphalt surfaces.” Inflate works with clients to provide optimal placement and design of interiors, as well as specific anchoring and wind requirements based on actual location. There are no maximum sizes for these structures, as segmented units can be combined to create extremely large spaces enclosed by fabric. The smallest size structure, according to Howell, is a 5-foot by 5-foot “changing room.”

New developments

One of the most interesting recent developments for portable fabric clad performance structures is the Soundforms transportable stage. Designed for high-performance acoustic requirements, such as orchestral and operatic concerts in open-air settings, Soundforms PLC’s stage comes in three sizes, each designed to accommodate standard performance groups ranging from small ensembles to full orchestras. The concept for the structure comes from world-renowned conductor Mark Stephenson, based on a custom-designed and constructed acoustical ceiling unit that hangs from a lightweight, aluminum truss system enclosed by fabric. Schematically, the motivation is to reproduce concert hall quality acoustics for outdoor performances, a very difficult prospect. Wind, jet planes, noisy service trucks and electric generators prevent hearing a performance as intended. The traditional park gazebo or wood-framed shelter stage just doesn’t cut it.

Stephenson collaborated with Arup Acoustics to create a finely tuned series of wood baffles hung from a truss as the main sound control system. This is enclosed by an aluminum truss-framed enclosure wrapped in white PVC-coated polyester fabric made up of eight inflatable cushions that create one structural unit. An interior liner of stretch fabric (the kind often used in theaters) is added to aid the acoustics. A blackout fabric is fitted between the liner and the outside fabric shell to prevent light seepage during night performances. Soundforms’ collaborative design team includes event promoter ES Global and fabric structure specialists Architen Landrell.

Material world

What types of fabric is most appropriate for portable structures? Again, the intended end use plays a big role in making the right choice for maximum efficiency and durability. For long term but temporary (seasonal, for more than a month), or traveling venues, some designers use PVC-coated polyester or LDPE-coated HDPE. For structures that need to be erected and taken down many times, such as air-supported structures or airbeam-supported structures, a coated ripstop nylon should suffice. If intended for multiple seasons, a more durable and highly flexible coated PTFE fabric is recommended. ETFE foil can be used for seasonal applications as a single-skin film. In many cases, if fabric is used in public spaces, it needs to be fire retardant, and FR coatings can be added to meet this requirement.

Expanding opportunities

Beyond the sort of everyday public venues like sports, art or festival events that have ready-made and modular fabric structures, there are many opportunities for creative design and fabrication. This trend follows the development of permanent fabric structures and is largely custom made to fit. The Australian fabricator, Pattons, works with many staging and film industry companies that need temporary structures, but always finds that, where custom designs are concerned, it pays to involve the client as early as possible. “We ask our clients to engage us from the very beginning, finding all requirements and working with them to deliver reliably on their project,” says Thomas Gastin, managing director of Pattons. “This includes high scale events like World Youth Day, The 2000 Sydney Olympic Games, The Commonwealth Games and The Asia Games.”*

As with most architecture, the unique requirements of location, usage and timeline of usage will affect the final design of portable fabric architecture. The possibilities are only limited by the imagination.

Bruce N. Wright, AIA, is an architect/journalist and the former editor of Fabric Architecture magazine.

*Gastin and his employees have put together a 12-point check list of characteristics that need to be considered when custom designing portable structures, including performance standards for extreme weather conditions, rigging requirements and installation sequence schedules. See Rigging Checklist sidebar.

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