While FRP panels serve a largely decorative purpose in many vertical construction projects, structural use of FRP has been more limited. Some fabricators are exploring ways to boost the structural properties of panels. Bill Kreysler, president of custom FRP engineering and fabrication firm Kreysler & Associates in American Canyon, Calif., has spearheaded numerous innovative projects in vertical construction, including 1,500 uniquely-shaped GFRP panels for the façade of the Lucas Museum of Narrative Art under construction in Los Angeles. “We’re currently working on a weatherproof wall panel [for another project] so FRP could be used as the building envelope as well as the decorative skin,” he says.
One area where FRP is more likely to see an uptick as a structural material is in use as a reinforcement in concrete foundations and masonry structures. Concrete, which has relatively low tensile strength, is typically reinforced with steel rebar to add greater strength for thinner, longer, less-supported slabs. However, as billions of dollars’ worth of crumbling infrastructure across the United States indicates, steel reinforcement has problems. Chief among these is corrosion. Although concrete may offer some natural corrosion protection, this wears down over time.
Corrosion resistance, of course, is one area where GFRP products shine. While the higher upfront costs of GFRP have delayed its widespread use, research and innovation in these areas are driving some of the changes that may soon open the vertical construction industry to greater use of GFRP-reinforced concrete.
The American Concrete Institute (ACI) Technical Committee 440 develops guides and standards for FRP Reinforcement, including ACI 440.1R-15, Guide for the Design and Construction of Structural Concrete Reinforced with Fiber-Reinforced Polymer Bars. “The 1R document is recognized not only in North America, but throughout the world as the document at the basis of this technology in vertical construction,” says Antonio Nanni, a professor of civil, architectural and environmental engineering at the University of Miami.
Four years ago, the ACI Technical Committee opted to not revise the document and instead embarked upon the lengthy process of developing a code that lays out mandatory language for how to appropriately design and build using FRP-reinforced concrete for structural applications. Upon its publication in 2022, the document – tentatively titled Code Requirements for Structural Concrete Reinforced with FRP Bars and Commentary – would be referenced by ACI 318, Building Code Requirements for Structural Concrete, the basis for the design of every reinforced concrete building in the country. Through the new code’s reference in ACI 318, it would become incorporated into the International Building Code (IBC).
Since ACI 440.1R was last updated in 2015, a lot has changed in understanding the science behind FRP in these applications, and the committee has worked through these advancements. Nanni notes that some of the safety factors have been relaxed due to greater awareness of material properties. For example, he points to growth in knowledge around creep rupture.
“Composites have a peculiar behavior when subject to sustained load,” Nanni explains. “They suffer static fatigue.” Creep rupture describes the material’s failure over time after sustaining constant uniaxial loading. ACI 440.1R-15 sets the coefficient for ensuring that this creep rupture does not occur at 0.2, or 20% of the FRP’s strength under immediate load. However, that number was derived in 2001 using limited test data and few standards around the materials or test methods.
“Today, we can safely say it’s 30%,” Nanni says, adding that some data indicates this number could rise considerably higher in the future. “This is very significant, in that we have made the use of composites more competitive with respect to steel. Not because we look at saving money necessarily – although that is one outcome – but because we have better science to address these issues.”
Code Challenges
For many firms, the larger challenge is meeting established fire performance requirements. Jesse Beitel, senior scientist and principal with specialty engineer Jensen Hughes, was part of the team that developed the first code requirements on FRP for the 2009 edition of the International Building Code. (In the 2018 edition of the IBC, this information is found in Chapter 26, Section 2613). The code development group was tasked with establishing requirements for decorative finishes based on existing code requirements, but faced new territory in adding the capability to use FRP on building exterior.
The committee ultimately determined that limited amounts of FRP, such as in cornices or millwork that make up less than 20% of the wall surface, would need to pass an ASTM E84 fire test. It’s a test that many of today’s FRP products can pass, says Beitel. However, he adds, “If you want to build an exterior wall and you want to use FRP as the wall covering and it’s more than [20%], you need to meet NFPA 285, Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Wall Assemblies Containing Combustible Components. That test is typically where FRP has a problem.”
Aljishi agrees that meeting this code is an area where companies worldwide continue to struggle. “The need to meet the code limits the number of firms [working with FRP] to the very few who have the competence and knowhow, particularly in fire codes,” he says.
He adds that the codes are critical in limiting damage as well as broadening use of FRP. “It’s an ever-evolving area of study for anybody who is looking at the field because the codes are always changing, and any time there’s a major fire like the one in London you get another type of code,” Aljishi says. The Grenfell Tower apartment fires to which he refers killed 71 Londoners in 2017 due to the rapid spread of the fire, attributed in part to the use of aluminum composite panels for cladding. Aljishi adds, “Even if you didn’t have a code, insurers are asking for their own code, which drives the field toward noncombustible materials.”
Leading firms work to meet U.S. codes and similarly stringent codes for the protection it affords architects and composite fabricators alike. “I hear a lot from the United States that Middle Eastern companies are like ‘cowboys,’” Aljishi says. “This is inaccurate. Here in the Middle East, it depends on the project, but they normally follow either ASTM or U.S. building code, European EN standards or British standards. The large landmark projects have very stringent norms that work here as they work in the U.S.”
Still, these norms are tough to meet, and it’s this challenge that Beitel predicts will keep FRP confined to small portions of façades for the foreseeable future. “[The industry has] got to do a lot of work with respect to formulations and doing the testing to verify that this works,” he says.
Innovation Strategies
Nanni notes that the existing codes aren’t meant to deter use of FRP in any application. “Chapter 1 Section 11 of IBC says that the intention of the model code is not to prevent innovation,” he says. “So if there is a technology that is being tested according to a set accepted criteria, and that technology shows compliance with intent of this code through an evaluation service report, then the building official is compelled to adopt it – or you might say, should consider it.”
The International Code Council Evaluation Services (ICC-ES) works with innovators to publish acceptance criteria documents that outline new criteria or revisions to criteria. Those documents, once approved during open public hearings or public comment through icc-es.org, can be used to apply for an evaluation report. AC454, for example, lays out criteria for use of FRP Bars for Internal Reinforcement of Concrete Members and is used to issue ICC-ES evaluation reports to applicants, allowing use of new technologies in construction. “This is a methodology for deploying innovation without having to wait for code development that obviously takes years and is a very long process,” Nanni says.
Still, these types of exceptions are most helpful for large-scale landmark projects. Making FRP as common a structural product as wood or steel will take easily accessible guidelines. “The next step is to get FRP written into the structural codes,” Kreysler says. “I always hear how expensive and hard this would be, but all we need is a definition of structural FRP. Simply being recognized as a material is half the battle. The next step is to define the properties.”
Getting FRP incorporated into building codes – and gaining public buy-in surrounding composite materials in vertical construction – gets a little bit easier with every new project in which composites play a role. “It’s a matter of getting contractors familiar with the material,” Nanni says. “It takes education.”
