NIST Industrial Impact

Company: Strongwell Corporation, Bristol, Virginia
Business: fiberglass products manufacturer
Number of Employees: 400 employees at this plant
(total of 1,000 employees at 4 plants)

With 40 percent of U.S. bridges considered deficient or obsolete, transportation officials and motorists long for relief from the relentless decay of steel and concrete that costs the nation billions of dollars for repair and replacement--even more if the endless construction-related traffic delays are counted. For some folks in Virginia, relief is finally in sight.

Among the most pleased are executives at Strongwell Corporation, which is in the final phase of a three-year NIST Advanced Technology Program project that has enabled the firm to overcome formidable challenges associated with manufacturing composite structures. Composites are hybrids of two or more materials that have long been attractive candidates for infrastructure applications because they are lightweight and resistant to rust and corrosion. Until recently, this idea has not gone far beyond the laboratory research stage because the materials are expensive and difficult to engineer into structures of appropriate shape and size with adequate stiffness and overall performance.

Strongwell now enjoys the satisfaction of having designed and manufactured 8-inch-high prototype bridge beams made of carbon- and glass-reinforced polymer composites that not only achieve technical goals but also are attracting interest from potential users, including a number of state transportation agencies and several industrial sectors. In fact, in an offshoot to the ATP project, the beams were installed in a rehabilitated vehicle bridge in Blacksburg, Va., in June 1997, providing an opportunity for demonstration and field testing.

Taxpayers are expected to be major beneficiaries over the long term, because although composites are two to three times more expensive than steel initially, the structures cost less to fabricate and install, and the absence of rust and corrosion should reduce bridge maintenance and overall life-cycle costs. "Hopefully, they are going to get bridges that last a heck of a lot longer and go in a lot quicker so there will be fewer traffic delays," says Glenn Barefoot, a Strongwell manager. Meanwhile, the company is not resting on its laurels; it continues to work toward the design and processing of a 36-inch-high beam.

The technical challenges so far have included enhancing the mechanical properties of the composite material, optimizing beam shape, and establishing design standards and load capacities. Strongwell achieved advances in both the material and beam shape. The material consists of glass and carbon fibers bound by a resin. The revolutionary shape is a "double-web I" or "modified box" beam in which two 8-inch vertical webs are connected by 6-inch-long flanges across the top and bottom. Transverse stiffeners are added inside the "I" parallel to the flanges. Carbon fibers were added to the flanges to overcome the challenge of insufficient stiffness, giving the beam a "modulus of elasticity" more than twice that of traditional fiberglass.

Strongwell also manufactured one beam using vinyl ester resin, which provides superior corrosion resistance, and another using phenolic resin, which is not as strong but provides superior fire resistance. "Without ATP funding, we could not have afforded this," says Barefoot, noting that phenolic resin is very difficult to handle because it must be processed at very high temperatures and 20 percent of the resin is lost to condensation. Prior to this project, the largest part made of phenolic resin was a 1.5-inch square tube, Barefoot says. With the help of the Georgia Institute of Technology, Strongwell optimized the beam shape for torque resistance, eliminating the need for braces. The beams performed well in tests for fatigue, creep (or stretching under tension), and strength under static loading.

Twenty-four Strongwell beams made with vinyl ester resin were installed successfully in the rehabilitated Tom's Creek Bridge in Blacksburg, which is one of the first vehicular bridges in the United States to use hybrid composites--containing both glass and carbon fibers--as the primary load-bearing structure. Jack Lesko, an assistant professor of engineering science and mechanics at Virginia Polytechnic Institute and State University, has long been interested in studying the durability of composites but frustrated by the lack of field applications. He and a group of other researchers and transportation officials finally convinced the town of Blacksburg to replace the aging steel-framed bridge with 20-foot-long composite beams covered by a wooded deck topped by asphalt. Lesko asked Strongwell for assistance, and, by chance, his timing coincided with the ATP project.

Other agencies involved in the Tom's Creek project include the Virginia Transportation Research Council, the Center for Innovative Technology, and a National Science Foundation-supported research center at Virginia Tech that focuses on high-performance polymeric adhesives and composites.

Lesko is impressed by Strongwell's accomplishments and excited to have the opportunity to learn whether composites actually live up to their promise. The bridge, located on a rural road near Virginia Tech, carries 1,000 cars per day, mostly commuters. Lesko plans to monitor bridge traffic, loads, and environmental conditions using a variety of techniques. Testing over the next decade will assess changes in the composite materials, which, although they do not rust or corrode, may undergo changes in weight, volume, or other characteristics, Lesko says. Test results also will be useful in establishing implementation standards for composite bridges.

Barefoot envisions Strongwell's new technology being used in a range of applications, including short-span bridges, offshore oil platforms, and industrial applications where corrosion is a problem. Outside of Virginia, the composite beams already have attracted interest from transportation officials in Ohio, Illinois, California, Pennsylvania, and Oregon as well as companies in various industry sectors, Barefoot and Lesko say. A major oil company has inquired about using composites in secondary structural members for offshore platforms, where light weight is a major advantage. Wooden deck manufacturers also are intrigued.

Strongwell's current challenge is to design and process 36-inch-high beams that will meet national transportation standards. As part of the ATP project, the company is building a new machine that will extend the capabilities of the composites manufacturing process known as pultrusion. The objective is to achieve 120,000 pounds of force--
more than they originally thought they'd need--to pull thousands of tightly packed fibers through a bath of polymeric resin and into molding and curing dies of the required size and shape. The need for the new machine was unexpected, but it is a challenge that, with the help of ATP, the company is ready to meet.

September 1997