I-5 bridge over Columbia could last a long time
PORTLAND — Absent a big earthquake or a catastrophic encounter with a too-tall truck or ship, the Interstate 5 bridge that now spans the Columbia River could stand almost indefinitely, a state inspector says.
It may need to.
If plans to replace the bridge don't advance by mid-March, Oregon Gov. John Kitzhaber has promised to pull the plug on it — after more than 10 years and $190 million spent.
The project is in trouble. The Washington Legislature decided last year not to participate, and that has raised concern in the Oregon Legislature, particularly in the Senate, about an Oregon-only project projected to cost $2.8 billion.
A new bridge project could take a decade to get going.
In the meantime, Oregon's state bridge engineer, Bruce Johnson, said the current bridge will need repairs and, in 15 to 20 years, a $75 million paint job.
“If you're willing to do those kinds of fixes and you have a robust inspection system like we have, you could almost say the bridge will last indefinitely,” Johnson told The Oregonian.
The Interstate 5 bridge linking Portland and Vancouver, Wash., is actually two spans.
The first opened on Valentine's Day in 1917 and replaced a ferry. It now carries northbound traffic. A toll, initially 5 cents for motorists and people riding animals, ended in 1929.
Its twin opened in 1958, with an initial car toll of 20 cents, retired in 1966 when the bridge was paid off. It carries southbound traffic.
Marc Gross, a former Army engineer, heads the full-time bridge crew of 10. Supporting the crew costs more than $1 million a year, split equally between Oregon and Washington state. Routine subcontracted repairs and maintenance are budgeted for another $1 million annually.
“Vibration is our biggest enemy,” Gross said. He hires a full-time electrician to keep connections tight and maintain the system.
Friction is a close second. Each year, the crew lubricates six miles of drawbridge cables by hand, applying about 3,200 pounds of grease. Another 4,000 or 5,000 pounds of grease lubes gears, bearings and other parts.
Then there are starlings, which flock in at night to roost or nest, with the expected consequences in droppings. Gross mounted orchard cannons along the bridge that fired at irregular intervals, but suspended the firing this year.
“It's taken me probably nine years of doing it,” he said. “I've depleted about 40,000 to 60,000 starlings down to under 1,000.”
The bridge's lift, which allows boats to pass, has been operating at half speed while a part is manufactured to replace a roller damaged recently when a strong east wind pushed the lift off track and it didn't reseat properly.
Johnson said that if the bridge were to see conditions that would qualify it as structurally deficient, repairs could be made. Among those are cracking of the steel floor system and corrosion of steel truss members and connections.
“The major issues that might make repair and rehabilitation of the bridges infeasible would be a major earthquake or a major impact from an over-height vehicle or a ship,” Johnson said.
It's unlikely a truck could hit a portal and collapse a span, as happened to the Skagit River Bridge last year, Johnson said. The Columbia bridge doesn't have the same kind of angled supports, he said.
An earthquake that geologists predict will hit Oregon one day with the force of Japan's 2011 quake could tip spans into the river, blocking ships, and engineers expect the drawbridge tower to buckle, sending 500- to 900-ton counterweights crashing through the deck.
Johnson said a seismic retrofit would be extremely expensive: a new substructure under the existing bridges for perhaps $500 million or $600 million, strengthened trusses and rebuilt drawbridge towers for several hundred million dollars more.
Information from: The Oregonian, http://www.oregonlive.com