The Cutting Edge: COMPUTING / TECHNOLOGY / INNOVATION : Herculean ‘Threads’ New Quake Reinforcement : Construction: Scientists say the carbon composite will help protect California’s bridges and buildings from collapse.
In its raw form, it looks like human hair wound onto spools. When woven into a shiny fabric, it almost seems suitable for a fashion runway in Paris.
It’s a carbon composite 10 times stronger than steel that scientists, manufacturers and government officials say will help protect California’s bridges and buildings from collapse when the next big earthquake hits.
“This is a third alternative to concrete and steel,” said Gilbert Hegemier, director of the Charles Lee Powell Structural Research Laboratories at the UC San Diego, where carbon composites are being tested. “It provides stiffness and strength at much less weight. That mitigates the earthquake problem tremendously.”
Had this technology been available a year ago, Hegemier said, it could have prevented six of the seven major bridge failures wrought by the 6.7-magnitude Northridge earthquake, which left 61 people dead and billions of dollars worth of damage last Jan. 17.
Jim Roberts, the chief building engineer for the California Department of Transportation, said carbon composites show the most promise for retrofitting the 11,000 California bridge columns in need of structural reinforcement.
“Carbon fiber is much stronger” than steel, which is widely used now, Roberts said. “It’s very expensive, but because it’s stronger, you use less. And it’s not as labor-intensive to install, so it should save money.”
Unlike steel, carbon composites strengthen bridge columns without making them brittle and vulnerable to collapse, said Gloria Ma(cq), executive vice president of Xxsys Technologies, a San Diego company that has developed a machine to wrap columns in carbon fibers.
Since heavy structures are more vulnerable to earthquake damage, the low- weight composites are an attractive alternative to retrofitting with steel, Ma said. Also, carbon composites dissipate energy better than steel and concrete, so they can protect buildings from crumbling and bridge columns from buckling.
The composite threads are spun from a petroleum-based plastic that is heated and stretched until the molecules “carbonize.” Before it can be used to wrap bridge columns, the threads are bathed in a glue-like resin, according to Ma.
Carbon composites were first developed in the 1960s, and until recently were used exclusively for high-performance military aircraft and satellite. As the prices have come down, however, the materials are finding their way into commercial airplanes, tennis racquets, bicycles and other products.
Retrofitting buildings and bridges for earthquakes is a new, billion-dollar market for the carbon composites industry, said John Weidner, director of composite structures for Hercules Inc., a Magma, Utah, company that is the nation’s largest producer of carbon composites.
“This is not only for highway column wrapping,” Weidner said. “There are lots of columns used in building structures like parking garages. It’s a very large potential market.” Bridge columns built before 1971 are in danger of crumbling because they don’t have enough horizontal hoop steel embedded in the cement. Traditionally, these columns are fortified with steel jackets.
But the jackets make the columns stiff and therefore more likely to break during an earthquake. Also, the process of welding the steel to the outer walls of the columns is labor intensive, time consuming and expensive.
Wrapping bridge columns with the hair-like carbon composites shows promise because it can be installed less expensively with a bright yellow circular machine called Robo-Wrapper. Developed by Xxsys, the Robo-Wrapper winds spools of carbon composite strands around columns more than 10 times faster than steel jackets can be applied, Ma says. Once the column is wrapped, the carbon strands are cured into a tough, protective shell as strong as steel, then painted to resemble gray concrete, she added.
Column wrapping is just months from qualifying to bid for Caltrans projects, according to Roberts, and he expects to have the first columns wrapped by summer.
The technology also shows promise for strengthening bridge decks, freeway sound walls and buildings, Hegemier said. When woven into a shiny fabric, the carbon threads work like a non-corrosive “structural wallpaper” that can be applied to reinforce weak structures.
Last year, UCSD researchers applied the structural wallpaper to a five-story concrete masonry building that had been damaged during a simulated earthquake. Tests showed the building was twice as strong with the carbon wallpaper than when it was initially built, Ma said.
In addition to retrofitting for earthquakes, Roberts said the composites could strengthen older, corroding bridges in other parts of the country.
“There are plenty of potential uses for this material, not just in California,” Roberts said. “Back east, you can use it to strengthen columns to keep them from cracking and breaking from corrosion from de-icing salt. You just clean them and wrap them with the material and they’re protected.”
Hercules already produces four million pounds of carbon composites a year, and Weidner predicted that if composites live up to their retrofit potential, “the demand for our product could increase by a factor of 10.”
It would also bring millions of dollars of business to Trans-Science, a La Jolla research company testing various recipes for carbon composites, said senior research scientist Santosh Arya.
“This is the start of a new technology,” he said. “If it’s successful, it can be applied to other areas, like buildings and ships. The potential is enormous.”