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Simple Steps on How to Specify FRP Composites for your Next Job

Simple Steps on How to Specify FRP Composites for your Next Job

By Dustin Troutman, Director of Marketing and Product Development, Creative Composites Group

Fiber Reinforced Polymer (FRP) composites have emerged as a top contender when it comes to construction material choices for America’s infrastructure. “FRP has been used in construction projects for more than 30 years, but over the last decade the number, size and complexity of projects has grown rapidly,” says Gregg Blaszak, president of Coastline Composites.  “Awareness has also increased among engineers and contractors about the ways FRP’s unique attributes can contribute to a project.”

Coastline Composites is a technical marketing and consulting firm with a focus on developing applications for FRP in the heavy and civil construction industry. The firm partners with leading FRP suppliers like Creative Composites Group (CCG) to offer cost-effective solutions to engineers, contractors, and asset owners. CCG serves major infrastructure markets from rail and bridge to utility and waterfront with design-build and structural fabrication expertise. 

FRP’s growing popularity is also being boosted by the Bipartisan Infrastructure Bill, which, in 2021, introduced innovative materials like FRP into mainstream procurement processes for the first time. In a May 2023 update, the bill earmarked $40 billion for bridges alone and $66 billion for passenger and freight rail. According to Blaszak, pedestrian bridges and passenger rail are two markets that have proved to be “the right fit for FRP.” 

“Lightweight is one of the biggest reasons FRP is selected for a project,” says Blaszak.  “For example, FRP has become the material of choice for the rehabilitation and repair of historic bridges due to their inherent weight restrictions. Cantilevering an FRP sidewalk off of an existing vehicle bridge accommodates bicycles and pedestrians without putting large dead loads on the bridge. It is also less costly and less disruptive than other options. And, in highly congested urban areas with limited access to stage construction equipment, FRP helps contractors accelerate installation. Time is money in construction and FRP saves contractors a lot of time on their projects”.

Aside from its lightweight and quick installation, FRP is not susceptible to deicing chemicals making it well-suited for bridge and commuter rail structures in cold-weather states.  “Traditional materials just don’t last in these types of applications,” Blaszak says. “Most engineers interested in specifying FRP understand the initial price point for composite material may be a little higher, but lightweight, rapid erection and corrosion resistance often lead to lower overall project costs.”

CCG’s proficiency in prefabrication of very large FRP panels offers another advantage. The ability to construct composite components beforehand means the supplier can coordinate design and construction specifications upfront during the fabrication phase of a project instead of at the job site—factors that also contribute to faster installation and reduced costs.

Specifying FRP for a bridge deck or rail platform can be challenging for several reasons. According to Blaszak most engineers are not experts when it comes to the design and detailing of FRP structures. Standard DOT specifications for large FRP structures don’t yet exist. Each project is usually handled using special provisions. Industry guides and specifications offer limited help. The most useful is the American Association of State Highway and Transportation Officials (AASHTO) Guide Specification for the Design of FRP Pedestrian Bridges. First published in 2008, the specification is being updated to reflect current best practices. The American Society of Civil Engineers also recently approved a standard for Load and Resistance Factor Design (LRFD) of Pultruded FRP Structures. 

“Composite materials are different from traditional construction materials,” says John Busel, vice president, Composites Growth Initiative, for the American Composites Manufacturers Association (ACMA). “Design guidelines are intended to help engineers focus on the important attributes of composites and construction techniques 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.

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