FIBER-REINFORCED PLASTICS MAKE DAM BREAKTHROUGH: FIRMS SEEK USES OUTSIDE MAINSTREAM

Comments Email Print

NASHVILLE, TENN. — People pushing fiber-reinforced plastics into infrastructure markets, take heart: A dam gate made of composites withstood the pounding waters of the Ohio River.

``It saw some significant abuse,'' said Pete Hoffman, who studies new, nonaerospace markets for McDonnell Douglas Corp.

The paper on the dam test was one of the more exotic infrastructure reports at International Composites Expo '97, held Jan. 27-29 in Nashville. Highway guardrails, reinforcing bars and the ever-growing composite bridge category continued to generate interest.

St. Louis-based McDonnell Douglas, more accustomed to building military fighters than river dams, designed the wicket gate using pultruded I-beams and plates bolted together to a steel beam structure called a strongback.

Researchers at the U.S. Army Corps of Engineers tested it for one year on a prototype dam on the Ohio River in southwestern Kentucky.

A wicket gate is a large plate, pushed up into position by a large hydraulic piston. When the river levels are high enough to allow boats to pass safely over the dam, the wicket gates remain in a retracted position. When the river drops, the gates are lifted into position to raise the level of water upstream. Water rushes through gaps between the gates, creating intense forces, Hoffman said.

The Army Corps of Engineers is looking to replace oak wicket gates. At the test site, the composite gate was set up alongside heavy steel plates.

Other than thin side panels being ripped away — probably by debris carried by the river — the composite dam gate held up well, Hoffman said.

``It didn't hurt anything structural,'' he said.

Mostafiz Chowdhury, an engineer at the Army Corps of Engineers' Waterways Experiment Station, said the river made the composite gate vibrate more than steel gates, but no damage resulted.

Hoffman said that next time, he probably would make the very large part by one of the resin infusion processes, to create a unibody design, instead of assembling it from pultruded parts.

Other speakers stayed on dry land during technical sessions at ICE, sponsored by the Society of the Plastics Industry Inc.'s Composites Institute.

Pultruded guardrails might line highways in the future — if they can be made cheaply enough, said Lawrence Bank, civil engineering professor at Catholic University of America in Washington.

But tests show that standard, vinyl ester tubes can work well, because of the way the pultruded parts deform. A guardrail is a rail supported by end posts. Upon impact, the guardrail immediately begins to deform, then acts like a cable as more stress is applied. The research showed the FRP tube continued to take the load without breaking, even as it began to tear along its underside. It did not fail, Banks said.

The desirable, controlled tearing happens because pultruded parts have unidirectional fibers, he said.

Banks said high cost — a big nemesis of infrastructure composites — means the tube would need very thin walls to have a chance. Steel guardrails sell for $3 a foot, vs. $11-$14 a foot for pultruded products.

Besides cost, just getting the attention of highway departments in all 50 states can be an overwhelming task.

Making that task less daunting is the Highway Innovation Technology Center in Washington. HITEC, part of the Civil Engineering Research Foundation, was created as a ``national first-stop service center'' to evaluate new products that do not have their own standards yet, said David Reynaud, project manager.

A firm with a ``market-ready'' product pays HITEC a $25,000 fee, plus costs for further testing, if necessary. HITEC gauges interest at the state level and thoroughly reviews the product before issuing a detailed report. Testing can be done by state transportation departments, private laboratories and universities.

``HITEC is probably the fastest way to get a demonstration project,'' Reynaud said.

HITEC projects include composite bridge wrap in California, an all-plastic stop sign, a heated pavement system and both aluminum and FRP bridge decks.

The lack of standards remains a major issue, speakers said in Nashville. As composites keep growing in construction and infrastructure, the industry will need fire standards, said John Schweitzer, technical director of the New York-based Composites Institute. He led a panel discussion on the subject.

One well-known advocate of new markets, Charles McClaskey of Reichhold Chemicals Inc., urged caution.

``We're in that dangerous period where the standards and codes have not been fully put together yet,'' said McClaskey, who is vice president of business development at Reichhold in Research Triangle Park, N.C.

Common test methods also should be a top priority, he said.

``It's almost impossible to talk about these products intelligently unless we can agree on how to test them.''

Until new standards are finished, firms need to police themselves, perhaps adopting voluntary standards, to avoid problems.

McClaskey was enthusiastic, but realistic: ``We need to be careful in how we commercialize and introduce these products, so that we don't blow it.''