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I-80 bridge gets quake upgrade

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Many of the 2,500-plus bridges in Utah's interstate and state highway systems could collapse in an earthquake.

State legislators might react the same way when a study now in the works reveals just how much it would cost to prevent the state's bridges from crumbling under seismic pressure.

The Utah Department of Transportation will have that research ready for the 2002 Legislature. In the meantime, UDOT and transportation departments in other seismically sensitive areas of the country are searching for inexpensive ways to strengthen old bridges to meet today's seismic codes.

The most promising method is being employed on the I-80 bridge above State Street as part of a federal pilot program.

Monday, crews from Gerber Construction began the two-day job of enveloping the bridge's 16 concrete-and-steel support columns with a carbon fiber wrap.

The carbon, or graphite, is mixed with an epoxy to create relatively thin sheets that form a new outer casing for the support columns, making them three times stronger than steel.

Larry Cercone, a materials science consultant for UDOT, said a severe earthquake would cause unprotected concrete around the steel rebar to explode apart. The wrap keeps that concrete in place, reinforcing the steel and preventing collapse.

The State Street bridge, built in 1966, is one of 22 deteriorating bridges on I-80 between State Street and Parleys Canyon being rehabilitated this year as part of a $10 million project. The work began in January and is scheduled for completion in December.

The project is designed to add 15 to 20 years of life to the I-80 bridges. Hopefully, that will be enough time for state lawmakers to come up with the estimated $900 million needed to completely rebuild the five-mile stretch of interstate. UDOT would like to begin that toward the end of this decade.

UDOT has been testing and evaluating the carbon fiber wrap for about four years. It tested the product on several old I-15 bridges before they were torn down as part of the I-15 rebuild.

The State Street bridge is not the only I-80 structure with the added seismic protection. Twenty-four columns beneath the I-80 bridge above Highland Drive were wrapped in carbon fiber in 1996.

UDOT project engineer Michael Fazio said it just made sense to employ the new technology on the State Street bridge as well because it is such a crucial link in the Salt Lake Valley road network. Its collapse during a quake would not only obstruct State Street but would prevent access to the new interchange of I-15, I-80 and U-201, now under construction.

All of the bridges on the 17-mile I-15 reconstruction corridor are being built to current earthquake standards. And while those bridges do not employ graphite, that is the wave of the future. Cercone said construction of an all-composite bridge, devoid of concrete and steel, is under way near Palm Springs, Calif.

Extending the life of the State Street bridge will cost about $600,000. About $350,000 of that expense, covered by a federal grant, is for the seismic retrofit. Work on the bridge, and lane restrictions beneath it, will continue for about three more weeks.

Carbon fibers, originally developed for rocket casings, can be found in fishing rods, golf clubs and military aircraft among other products. Those used on the State Street bridge were made by Hexel Corp. of Magna.

Sam Musser, UDOT's research program manager, said the cost of using carbon fiber wraps for seismic retrofits should decrease as more construction companies offer the service. Still, it may cost the state millions of dollars to retrofit just a few of its oldest bridges.

Musser believes the current UDOT study will justify the practicality of such work. It's a lot cheaper to bolster an old bridge to withstand an earthquake than to build a new one after a quake hits, he pointed out.

"All the seismic states are doing this kind of a study to see which bridges are a priority, so there are a lot of people looking at this (carbon-fiber technology,)" Musser said.

Still, state lawmakers may want to brace themselves for a financial shock wave.


E-MAIL: zman@desnews.com