CompositesWorld
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JULY 2016 46 CompositesWorld FOCUS ON DESIGN somewhat subjective, but in the end, we decided to make the seams visible," he says. He likens them to the seams of a football, noting that they look purposeful and, therefore, like a natural feature of the structure. Putting the design to the tests In terms of the materials and laminate, Humphries recalls, "It's hard to say, 'we did this frst,' because of the simultaneous nature of the trade studies and interplay of factors," but he points out that, sometimes, a single factor overwhelmingly drives a design decision. In the shroud's case, that was the NFPA 285 fre-rating test all composite mate- rials must pass to be certifed for installa- tion on commercial structures 12.2m/40 ft or taller (see Learn More). Per the archi- tects' specifcations, the laminate also had to earn a Class A rating (smoke/fame spread) to ASTM E84. Meeting these requirements dictated selection of a phenolic resin. Before a specifc phenolic could be selected, however, a determination had to be made about the fabrication process. Tis, in turn, required fnalizing the shroud's dimensions, including the length and thick- ness of the component panels, how the panels would be attached, as well as the types of reinforcement and the specifc orientation of the layup needed to meet surface fnish and load requirements. Initially, several fabrication processes were considered, but in the end, vacuum infusion was selected over wet layup and prepreg. Aside from health and safety issues, wet layup is difcult, in large part, due to resin pot-life problems. A prepreg, on the other hand, requires a higher cure temperature and more expensive tooling. Also, the availability of proven, infusible grades of glass and phenolic resin tilted the selection in favor of vacuum infusion. Tat led to selection of Cellobond J2027 phenolic resin supplied by Hexion Inc. (Columbus, OH, US), with Cellobond Phencat 382 catalyst, which provides a pot life of up to 4 hours. Before proceeding to a fnal drawing, a battery of tests was conducted by Intertek Testing Services (Mississauga, ON, Canada) to select a laminate that would meet all the mechanical proper- ties requirements and provide designers with a structural proof of compliance. Humphries says CONSTRUCT typically specifes a laminate using statistically generated A-basis strength allowables, which by defnition provide a 95% confdence that 99% of the fabri- cated parts will equal or exceed that strength value in practice after the product is installed. Fire-rated for four stories plus Because the structure exceeds four stories in height, the building code required testing to the NFPA-285 fre/smoke performance standard for "high-rise" architectural structures. The test entails measuring the fame spread of this 6.1m/20-ft high panel, with an open window, comprising the laminate used in the construction of the shroud. Source | CONSTRUCT Read this article online | short.compositesworld.com/LTUShroud For background on changes to the IBC and the NFPA 285 testing requirements, see CW's feature titled, "Architectural composites: Rising to new challenges" | short.compositesworld.com/ArchComp SCRA closed its separate CONSTRUCT operations after the LTU project was complete. But for more information about the LTU installation, contact Micki MacNaughton, SCRA press contact, at micki.macnaughton@scra.org. Dave Humphries can be reached at david@humphries.com. Five panels infused from one tool Each of the shroud's fve panels was fabricated via resin infusion at JRL Ventures (Cape Coral, FL, US), which also made the single tool used to mold the panels. Each panel was infused with phenolic resin in about 30 minutes, and cured at 65.5°C for 30 minutes, followed by a post-cure for 2 hours at 74°C. For mechanical connection of the panels, integral 90° fanges were molded on the sides of each panel with the aid of removable fences. Source | CONSTRUCT