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Airtech

Composite Shelters Keep Transit Users Cooler

10 September 2010

Designing a bus shelter for a desert climate is serious business that strives to protect waiting passengers from the danger of excessive heat. An Arizona State University study concluded that the heat inside a traditional metal bus shelter can rise above 140°F (60°C).

A shelter solution created by architect Jeff Jarvis of TranSystems Corporation integrates a fiber-reinforced polymer (FRP) composite grid structure into a unique microclimate system. The color of the composite was optimized in a cooperative effort between Fibergrate Composite Structures, manufacturer of Fibergrate panels, and AOC, supplier of Chroma-Tek colorants for composites.

The performance of the composite-based bus stations for the City of Mesa, Arizona, USA, has been so positive that the Valley Metro Regional Public Transit Authority has expanded its use to the next series of stations built in Chandler, Mesa and Gilbert.

The shelter structure is based on composite because the material does not conduct heat the way metals do. The design calls for composite grating panels to be used for vertical walls and the roof to take advantage of the grating’s inherent grid pattern.

The grid is “softer”

“The grid design is ‘softer’ than a hard, solid mass,” Jarvis said. “The grid in the ‘fiberglass’ [composite] is much more open than the perforations that are typically used in metals. The grid provides shade while also allowing air to flow through.”

The panels for the shelters were made using Fibergrate’s unique manufacturing process, which automatically places continuous fiberglass roving into the channels of a special open mold. The channels are between raised partitions that give the mold the look of an inverted waffle iron. After the high-strength fibers in the mold are resin-impregnated, the resin cures into a crosslinked solid to form a structural composite.

The moulded panels are corrosion-resistant and fire-retardant, have a high strength-to-weight weight ratio, and can withstand high wind loads. In addition to referring to data generated by standard tests, Jarvis subjected demonstration panels to “real world” situations. For example, Fibergrate samples successfully withstood full swings of a baseball bat and torching from a high-powered portable lighter. Furthermore, Jarvis says, the surface of the molded Fibergrate grating panel is not affected by standard anti-graffiti cleaning materials and equipment.

Landscape trees combine with the composite panels to create a microclimate system that casts shade on waiting passengers. The trees are Desert Museum palo brea, a drought-resistant, U.S. Southwest native species that has been hybridized to eliminate thorns. The system is designed to ensure that at least six of the ten available seating locations will be in shade at any given time of the day.

Colour is critical

“The colour is critical to the application,” Jarvis states. “Green makes a statement. It is psychologically cooler and blends with the native trees. The value of the green has to be absolutely neutral to be able to radiate heat away and to allow bus drivers and others to see inside. If the green is too dark, the view is hidden. If the green is too light, the view has too much glare.”

To achieve the precise color that works best, Fibergrate asked AOC to provide three different custom-color cast resin samples made with Chroma-Tek pigment dispersions.

”We have a long history with AOC’s colorants unit,” said Darryl Moczygemba, Director of Corporate Quality and Supplier Relations for Fibergrate. “Working with our AOC sales representative Eric Stuck and AOC color expert Mark Harber, we were able to provide the architect samples within the very short time frame we had available.”

“We had to respond quickly,” said Harber, Business Manager - Open Mold Non-Reinforced, “but we knew we could push it through. We ensure that the carrier resin and pigment dispersion mixture is homogenous and that carrier resin reactivity is totally compatible with Fibergrate’s processing resin and UV stabilization system.”

John Sauer, Territory Manager for Arizona and Southern California added: “We wouldn’t be able to do this if it weren’t for AOC’s technical support. And the pigment dispersion that went into production is exactly the same as the dispersion for the approved sample. I wouldn’t say Chroma-Tek consistency is good. I’d say it is excellent.”