Construction facts and figures released
In its final update to area residents at the Oregon City-West Linn Arch Bridge project, the Oregon Department of Transportation shared some statistics provided by the contractor, Wildish Standard Paving, to illustrate the work done on the project.
Schedule The project is 99.99 percent complete and will finish ahead of the final contract date of March 31. In addition, the reopening of the bridge to traffic was on time after the 21-month closure. On Dec. 20, the replica lights were re-installed. They had been sent back to the manufacturer to increase their weather resistance. After the re-installation, the lights were left on for a seven-day burn-in (24/7) test. ODOT has received positive comments from local residents who were happy to see the lights back on. The only item remaining to be completed is the installation of some small signs, which will occur in late January. There will be no further impact to bicycle, motor or pedestrian traffic.
The contractor and the project Wildish Standard Paving is proud of its safety record on this project. There was no time lost to injuries during 61,000 hours of labor. This project employed a workforce of carpenters, steel workers, concrete finishers, equipment operators, truck drivers, painters, welders, electricians, tug boat operators, steel fabricators, concrete precast fabricators, sign fabricators, concrete suppliers, asphalt suppliers, materials testing technicians, project inspectors, engineers, structural engineers, traffic engineers, shuttle bus drivers along with other laborers and a variety of other project-related staff. Final estimated project construction cost $14.9 million. The total construction work lasted 35 months, from its start in July 2010, until final closeout in the spring of 2013. For nine months, Wildish employees worked double shifts to finish the project on time. There were up to 40 people working at one time including the subcontractors. The nature of the work and tight spaces precluded more workers on the bridge at any one time. The total project utilized 61,000 hours of labor. The painting of the bridge both inside and outside took 7,200 hours of labor. The historic replica lights on the bridge were patterned after one of the original fixtures was found on Atkinson Memorial Church in Oregon City. It is thought they were removed from the bridge in the mid-20th century.
Gunite removal On the steel arches, 18,000 square feet of old gunite was removed and replaced. The contractor purchased special hydro-blasting equipment for gunite removal and used a variety of techniques to remove it. Around 6,000 hours was spent removing gunite. Water pressure of 400,000 pounds per square inch was required to blast off the old gunite from the bridge. More than a million gallons of wastewater was collected, cleaned and treated on the project from various aspects of hydro-blasting including deck removal and bridge cleaning. More than seven barges, three tug boats and diving services were used preventing debris from falling into the river. Johnson Western Gunite Company worked about 7,200 hours to apply the new shotcrete.
Concrete and steel repair More than 1,000 square feet of concrete were repaired. Approximately 350 cubic yards of concrete were replaced on the bridge rail, bridge deck, sidewalks and columns. Railing: More than 1,600 linear feet of new precast concrete, steel reinforced railing were installed. More than 1,000 bolts were replaced. Five hundred forty corroded rivets were replaced with 3/4-inch-diameter high strength bolts. Approximately 30,000 pounds of structural steel were removed and replaced. Structural steel is a steel beam, column and plate used to support the bridge loads. Approximately 54,000 pounds of new reinforcing steel were used. Reinforcing steel or rebar are rods of steel embedded in concrete to give the concrete flexibility. Below the bridge deck, eight steel bridge stringers were replaced due to corrosion. Stringers are the support beams that run the length of the bridge. In addition, 32 stringers, with less corrosion, only needed repair. Bridge roadway A micro silica concrete deck overlay was installed. This is structural concrete that is less permeable to water and therefore reduces the potential for future corrosion of the steel under the bridge deck. Steel seismic cables were installed under the West Linn and Oregon City approaches to the bridge, tying the bridge decks super structure to top of the columns. The bridge supports a natural gas line, communications lines and the sanitary sewer line that go between Oregon City and West Linn. These services had to be maintained during the rehabilitation project. Some of the lines were moved to enhance the historic features and to make these lines less visible.
Facts for engineers and construction geeks The project involved installing 2,200 galvanic anodes, or sacrificial anodes, to help avoid future steel corrosion of bridge members and rebar. This is like you might install on your outboard boat motor. They are a small piece of zinc metal that is about the size of a deck of cards. This is electrically connected by wires to rebar or other bridge steel. This is a sacrificial piece of metal that will corrode before the bridge steel corrodes. Teflon sheets were installed between the bridge girder bearing surfaces. Girders are similar to stringers but span between the columns. The girders sit on top of crossbeams that sit on top of the columns. A Teflon sheet was placed between the girder and crossbeam to help allow girder to expand and contract with hot and cold temperatures while column stays stationary.