Contractors began preservation work in September on the Siuslaw River Bridge, one of numerous bridges designed on the Oregon Coast by Conde McCollough, Oregon state bridge engineer from 1919 to 1935.
Contractors began preservation work in September on the Siuslaw River Bridge, one of numerous bridges designed on the Oregon Coast by Conde McCollough, Oregon state bridge engineer from 1919 to 1935. The $14.2 million project is expected to take four years to complete with the main components including cathodic protection, new bridge rail and pedestrian improvements, specifically, ADA ramps on each end.
The bridge, opened in 1936, spans the Siuslaw River in downtown Florence and is listed on the National Register of Historic Places. Hamilton Construction of Springfield, Ore., won the construction bid. The first task is to assess the damage, said Rick Little, spokesman of the Oregon Department of Transportation.
“The contractor will go through and check for any damaged concrete and exposed rebar,” Little said. “That’s what they are trying to protect, the rebar. Moisture can get in the concrete and to the rebar, even while it is seemingly protected by concrete.”
Once the contractor has identified the corroded rebar and structural steel within the damaged concrete, they’ll use a system of cathodic protection to coat the rebar.
“Whenever there is corrosion there is an actual charge emitted in the process of the corrosion,” said Little. “What this system does is it transfers that electrical charge to the zinc and the zinc then is sacrificed rather than the steel reinforcement bar.”
The cathodic program has been really successful with other bridges and also is the accepted technique on lighthouses and in tanks, said Jeff Lange, ODOT project manager.
“Instead of corroding the interior structure, the moisture and salt content from the harsh weather corrodes the surface,” Lange explained. “The zinc itself doesn’t corrode. The color of the zinc coating is similar to a newer concrete look. Esthetically it’s going to look new and fresh.”
The most difficult part of the cathodic protection is figuring out how to hang the enclosures to form the structure.
“The enclosures are needed to apply the molten zinc, to both protect environment from anything getting out, and to control the environment internally so they don’t have moisture and temperature problems,” said Lange. “The enclosures also muffle the sound.”
This contractor is opting for an approach somewhat different from previous projects.
“The typical way is to build a work platform below the bridge and build containment structures and access it through the work bridge,” Little said. “On this project, instead of building a work deck the length of the bridge from which they would supply the containment structure, they are going to build a moveable containment structure and supply it from a barge when it is over the river. This way there is much less of an environmental impact. They may have multiple containment structures, and leap frog over each other. The barge will supply equipment and materials. This is another example of how ODOT will take these projects and design them and put them in motion, but once it gets in the hands of the contractor and they let the creativity flow, they can often think of different ways of doing things.”
Workers also will replace the bridge rails with what is referred to as a “stealth rail,” which recreates the historic look of the rail, but brings the strength to modern standards.
“The implication of the word stealth means basically it looks historic but it has the hidden strength,” Little said.
They also will be upgrading the deck to better withstand seismic activity. It’s not an extensive upgrade, Little said, but an important one.
“As I understand this one, we are securing a key location beneath the deck to the substructure.”
Heavy equipment on the job includes a 40-ton (36.3 t) P&H Omega RT crane operated by Great Western Corporation of North Bend.
“All the rest of the really large equipment is fixed,” said Little. “The HVAC equipment, compressors and generators are all trailer mounted. The balance of the equipment is small, such as a couple Xtreme and Gehl 8 to 10k reach forklifts and a small Genie 5519 reach forklift. By eliminating the work bridge the size of the equipment is reduced dramatically. A 5519 weighs less than 10,000 lbs. That will be our most utilized piece of equipment.”
Work on the bridge will continue year round, but is not expected to interrupt boat traffic below or vehicular traffic on the roadway.