|RESTORATION OF PATTERSON BRIDGE PLANNED|
|March 28, 2001 12:00 am|
GOLD BEACH The $15 million restoration of the Isaac Lee Patterson Memorial Bridge across the Rogue River was the subject of a community meeting Monday night.
The bridge was described as the Grand Old Lady several times by Engineer Frank Nelson, who helped develop the cathodic protection system which will protect her.
Like many of the historic Oregon Coast bridges designed by Conde McCullough, the bridge is rusting from the inside out.
Ever since the bridge was built in 1932, weather has been forcing salt and moisture through the concrete into the steel reinforcing rods.
Nelson said the steel deep inside the bridge is still sound, but rebar within three inches of the surface is rusting. The expanding rust cracks the concrete and jacks it off the bridge.
Lose enough steel and concrete, said Nelson, and the bridge cannot stand.
Thats what happened to the Alsea Bay Bridge at Waldport, and the Oregon Department of Transportation had to take it down.
Nelson said the public sent a clear message that the department was not to lose another of the five big Oregon Coast bridges constructed by the Works Progress Administration.
Nelson headed the nine-person team that borrowed from nautical preservation techniques to come up with a solution. He said it was known at the time of the American Revolution that some metals corrode faster than the metals boats are made of. By 1824, zinc was used to control the corrosion of the copper bottoms of boats.
Zinc corrodes faster than steel rebar. Nelsons team discovered that if a concrete bridge was coated with zinc, and both it and the steel rebar were electrified, the zinc would corrode instead of the rebar.
The applicator is a cross between an arc welder and a sand-blaster. Zinc wire is melted and blasted onto the concrete surface in a thickness of 20 1,000ths of an inch.
It will be tested for bonding so that every part of the bridge will be completely coated. The zinc is the color of concrete, so the bridge will look much as it did when it was new, said Nelson.
Zinc turns a bit lighter and whiter as it corrodes. Nelson said as time passes, bird droppings and other atmospheric effects will change the appearance of the bridge more than the zinc.
When the zinc is completely corroded away in 30 years, the bridge will get another coat, and can be protected indefinitely.
The system has been applied successfully to five major coastal bridges since 1992.
Nelson said the bridge will be restored like a classic car. Decaying concrete will be replaced before the bridge is hot-coated.
The top deck will be resurfaced with high-density concrete. The old concrete railing will be replaced by concrete-coated steel.
Thin wire mesh will protect children from falling through the arches in the railing.
One of the main piers will be shored-up, and the bridge will be retrofitted to withstand a 6.0 earthquake, such as the one that recently hit Seattle.
Best of all, the bridge will not be altered visually. Everything new, including the power source for the anti-corrosion system, will be hidden under the bridge.
The old railing could be kicked off by most people, said Nelson. The new one will be visually identical, but could stop a truck and not give more than a quarter inch.
The bridge will look more original than it does today, because the water line that now runs alongside the railing will be split into two smaller lines and placed under the bridge.
Like anyone else, the transportation department had to obtain environmental permits for the project.
Project Manager Ray Cranston said the work under the bridge will be done from temporary working bridges. A full moveable enclosure will make sure no foreign material falls into the Rogue River.
He said just as much care will be taken to protect the tourist economy of Gold Beach. To test for traffic delays, Cranston closed off a lane of traffic during a Friday last August.
He found if only one span length of bridge was closed, traffic never backed up. Two spans was too many, so only one lane of one span will be closed at a time.
Cranston said delays should be no longer than at the painting project on the Thomas Creek Bridge: about three to five minutes.
If delays take longer than that, work will be switched to the off-season or night. No lanes will be closed at fair time. Pile driving will be done in the winter to minimize disturbing motel guests.
Cranston said Senior Project Inspector Dave Fletcher will be on site to get the four-year project started, and will work with the chamber of commerce and motels to make sure tourism is not impacted.
In fact, said Cranston, the $15 million project should boost the local economy. About 40 people will be working on the project at any one time, and many will move to Gold Beach temporarily and need food and housing.
Hardware stores will see a lot of business, said Cranston, as contractors look for last minute tools and supplies. The zinc will not be purchased locally, but the concrete could be.
Crane workers and riggers will be hired locally, as well as carpenters, and flaggers. Fletcher will need an office, and he and Cranston personally promised they would have an impact on the sale of sporting goods.
Cranston said department employees are begging to work on the project. Part of the appeal is the opportunity to live and work in such a beautiful setting. Cranston said it is also a privilege to work on such a unique and impressive bridge.
Department Historian Leslie Schwab said the Patterson bridge is unique even among McCullough bridges.
It was the first bridge in the United States to use the French Freyssinet method of arch decentering and stress adjustment of arch ribs.
As a result, the arches are thinner and more delicate looking than other McCullough bridges, but just as strong.
Companies had to prequalify to bid on the project, and the bid will be awarded in April. Only three companies qualified, and their subcontractors were screened for bridge restoration experience. Construction should begin by July.
The 40 citizens in attendance couldnt come up with a question to stump the transportation departments assembled experts.