CompositesWorld
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OCTOBER 2015 CompositesWorld 112 FOCUS ON DESIGN Pontoon fabrication During pontoon fabrication, Kenway Corp. applied techniques it had used previously for "marine camels" — giant foating fenders that protect piers in submarine berths (see "Learn More"). "Te same fberglass, vinyl ester resin and fotation foam were used as on camel fenders," says Kenway senior project engineer Jake Marquis. After design completion, the Kenway team had to calcu- late the number of internal members necessary to meet stifness and strength requirements in the pontoon sections, and then determine the pontoon shell thickness. Kenway molded 10 identical pontoons, using a hollow mold constructed of CNC-machined plywood frames (see photos, top left and center). First, the bottom and sides of the hull were molded by laying in dry fberglass, supplied by T.E.A.M. Inc. (Bristol, RI, US), and vacuum-infusing the layup with vinyl ester resin from Interplastic Corp. (St. Paul, MN, US). After cure, sepa- rately infused interior bulkheads were bonded into position using two-part Plexus methacrylate adhesive (ITW Plexus, Danvers, MA, US) to form a grid that was subsequently flled with fotation foam before an infused fberglass top was bonded to the pontoon hull. During fabrication, ASCC ran tests to verify the material proper- ties of the composite laminates produced at Kenway for construc- tion of the pontoons, and a series of tests to evaluate the pin- bearing strength of the composite fanges that connect the sections of the bridge. "Tese results were used to verify that the fanges had the strength to perform as required for the bolted joints," says Tom Snape, ASCC research engineer. "After fabricating the pontoons, the Kenway crew staged them in their yard, matching up the [splice-]plates and drilling more than 1,000 bolt holes before delivering them to the bridge site," Marquis says. Te estimated weight of a single raft (two pontoons), including foam flling, but no attachment hardware, is 11,570 kg. Bridge installation At the bridge site, before pontoons began to arrive, crews removed the old bridge structure and installed coferdams before constructing new concrete abutments. "Putting a coferdam on a ledge [at one end] was challenging, but we overcame it," says Paul Holloway, project manager at Miller Construction (Windsor, VT, US). Beginning in August 2014, Miller Construction began joining pontoons and launching rafts, as they arrived. Pontoons were delivered to the bridge site two at a time, as they were molded and fnished, over a four-month period, Holloway says. "We made a fabrication table out of steel girders and when the pontoons showed up on the fatbed truck, we unloaded them with a crane and put them on the fabrication table where they were bonded together," Holloway says, using Plexus methacrylate adhesive. "Tree tension rods passed through both pontoons, with a nut on each end to squeeze them together while they are glued," explains Marquis. "Crews spliced them together and installed the last raft in early December just before the lake froze," Holloway recalls. Although the pontoons are expected to last for 100 years, the modular raft design of the Brookfeld Bridge will permit relatively easy maintenance or replacement of pontoon sections in the event of damage without pulling the entire bridge out of the water. "Our project created design criteria and specifcations for FRP pontoon construction that could be used as a basis for future projects with similar characteristics," Olund says. But he predicts the most direct technology transfer for the foating pontoon system likely will be in the marine industry, for foating docks, wharfs, barges, pedestrian bridges and temporary military bridges. ABOUT THE AUTHOR Johanna Knapschaefer, a bilingual (English/Japanese) writer based on Boston's North Shore, writes about design and construction of buildings and infrastructure as a correspondent for Engineering News-Record, McGraw-Hill Construction, Architectural Record and other publications. CNC-accurate tool design Plywood stations cut with a CNC router are pieced together and decked with more plywood to form the frst half of the pontoon hull mold. A rotary laser level is used to ensure the 15.54m mold is straight and level to within 1.75 mm. Source | Kenway / Photo | Jake Marquis Pontoon tool surface prep The plywood mold is covered with fberglass, which then will be sanded and bufed to a glossy surface. Molded pontoons will be capped on the ends and enclosed on top, reinforced inside and flled with foam. Source | Kenway / Photo | Jake Marquis Rafts in the water and ready Here, the fve 15.54m long by 7.01m wide rafts — each formed from two buoyant FRP pontoon structures, assembled back-to-back — are in the water and assembled, ready for connection to land and wooden superstructure. Source | Miller Construction Read this article online | short.compositesworld.com/FloatBridg Read more about UMaine's "bridge in a backpack" online in "Bridge cost cut with inflatable arches" | short.compositesworld.com/DwM3fIlT Read more about Kenway's submarine "camels" online in "Composite submarine camels win with long-term durability" | short.compositesworld.com/fU1KgKnR