that will both educate and hopefully prevent over-designed and costly decisions when specifying composites. This results in better, more efficient, cost-effective solutions.” For engineers who want to source FRP, the first step is to create a special provision that recognizes the design and detailing of a composite structure is the responsibility of the FRP manufacturer. “It’s critical for an engineer to reach out to an FRP manufacturer like CCG when evaluating FRP for their project,” Blaszak says. “Getting the supplier involved early on in the process prevents potential headaches downstream like specifying a product that can’t be manufactured, inadvertently sole sourcing a product, or not meeting budget expectations.” Pultrusion and vacuum infusion molding are the two most common fabrication methods for heavy and civil infrastructure projects. Both methods have pros and cons, so it is important to work with an FRP manufacturer to help determine the appropriate method or “basis of design.” “To avoid a pultrusion or infusion molded bias, it’s always a good idea to contact more than one manufacturer or one with the capability for multiple fabrication methods,” Blaszak says. CCG’s engineered FRP panels use a fiber reinforced foam core encased by two fiberglass facesheets to produce a sandwich structure. The closed-cell foam creates the prefabricated bridge panel’s shape and eliminates the potential for open cavities where water could collect. The durable decking panels support a uniform load of 90 psf for all designs and comply with AASHTO regulatory standards for pedestrian bridges. CCG’s FRP panels can also incorporate custom shapes and functional features such as crowns, cross-slopes, curbs, and drainage systems. For decks or platforms made with pultruded profiles, the supplier uses a continuous manufacturing process to produce high- strength, lightweight FRP structural profiles such as angles, C-channels, and I-beams. Fiberglass reinforcements in the form of roving and mats are saturated with resin and channeled into a heated die. The profile exits the die in the form of the desired cross section or shape. Pultruded profiles have a higher tensile strength than conventional steel yet are lighter weight. Once the “basis of design” is selected the special provision can be written. “Most specifications are a hybrid of prescriptive and performance requirements,” Blaszak notes. The engineer should prescribe the design criteria (loadings, deflection limits), material types (fiberglass, vinyl ester, or polyester), pay basis, warranty requirements, validation testing, and acceptable tolerances. The FRP manufacturer will determine panel composition, thicknesses, and connection details to meet the project’s performance requirements. A basic list of “do’s” and “don’ts” can help avoid some common pitfalls. The engineer should prescribe project loads, especially unique loadings not found in industry codes and guides, as well as criteria unique to the project such as maximum allowed weight for FRP or fire/flame/smoke requirements. The FRP manufacturer is responsible for the design, but the engineer should require the supplier to submit test results for unique structural details to validate performance. The engineer should also request that the FRP manufacturer submit calculations and shop drawings sealed by a local engineer with experience in the design of FRP structures.
Photo Credit: Arcoro
All FRP bridge decks and commuter rail platforms require a polymer overlay to provide a sufficient degree of wet and dry slip resistance for pedestrians. While the FRP deck manufacturer should specify the non-slip overlay that works best for their FRP decking, it is the job of the engineer to specify the wet/dry coefficients of friction. The FRP manufacturer should be required to submit a 5-year performance history of 10 or more overlay installations on similar projects. For example, a public transportation agency for a commuter rail will want to verify that the overlay selected for a heavily trafficked rail platform has been used on other platforms, not just a remote trail bridge. Most importantly, the engineer should specify that the non-slip overlay be applied in the factory versus the field. For commuter rail platforms, tactile warning tiles should also be factory-applied. Factory application of these components improves quality and accelerates installation. Like any other material FRP structures are connected to and supported by a concrete or steel superstructure. The FRP manufacturer should be tasked with the design and detailing of the connections, but the engineer is responsible for specifying stainless steel connection plates and hardware to match FRP’s longevity. Blaszak cautions engineers not to specify tolerances that are too restrictive and incompatible with the manufacturing method. Construction tolerances should not be any more restrictive than those used with precast concrete structures. Details like drainage, sloping surfaces, and joint materials should be the responsibility of the FRP manufacturer, but the engineer should require joint materials to be installed by trained and certified specialty contractors. Close collaboration between the engineer and FRP manufacturer during the evaluation and design phase are essential steps that can lead to a project that is successful and on-budget. “Specifications are demanding to write and tedious to read but often can make or break a project,” says Blaszak. FRP’s performance benefits coupled with the growing trend toward sustainable practices has incentivized the industry to expand adoption of FRP as a construction material. Like steel and other traditional materials, FRP is taking its rightful place as another tool in the engineer’s toolbox.
Dustin Troutman is the Director of Marketing and Product Development for Creative Composites Group.
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October 2023 csengineermag.com
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