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2014WinShotcreteEMag

2013 Outstanding Repair & Rehabilitation Project The Oregon City Arch Bridge By Marcus H. von der Hofen T31, 2012, by the Wildish Standard Paving on each side and the added bonus of restroomsthroughout. This all supports a roadway deck18 ft (5.5 m) across, curb to curb, with a sidewalkhe Oregon City Arch Bridge Rehabilitationproject was officially completed on October Company. Dedication to quality and profession- located at the piers under the sidewalk at each end. alism, along with a true partnering between In April 2010, Wildish Contractors was owners, contractors, and suppliers, helped find awarded the contract for the rehabilitation of the ways to solve problems that could have easily Oregon City Bridge. The goal was to upgrade the turned the project into overwhelming confronta- structure to replace structurally deficient compo- tion and failure. nents and accurately replicate the details and Originally completed in December 1922, the architectural features to keep the original appear- bridge spans the Willamette River between Oregon ance of this historic icon. A great deal of work City and West Linn, OR, and is a beautiful landmark was necessary to carry out this upgrade within of the region. It was designed under the direction of the short time frame of only 2 years. State Engineer Herbert Nunn, who adopted and During my first visit to inspect the bridge, I must carried out the plans of State Highway Engineer say I was more than a little overwhelmed by the C. B. McCullough. McCullough’s signature craftsmanship of this structure. It was and still is detailing is evident in the arches, obelisk pylons with amazing to me. The quality of the gunite that these sconce light fixtures, ornate railings, and Art Deco crews produced so long ago is impressive. Not that piers. It is believed to be the only bridge of its kind there weren’t any problems, but for the most part, in the entire United States—a through-deck steel the gunite has held up incredibly well over the years. arch covered with shotcrete that incorporates con- The finish, the consistency, and, again, the overall crete spandrel columns, corbels, a sidewalk, deck craftsmanship produced by the crews must have approach spans, and a bridge rail. made subcontractor Lanning & Hoggan immensely The bridge is 900 ft (274 m) long, including the proud. Most of the deficiencies I saw really didn’t viaduct design approaches. The center section of the have anything to do with the gunite but were inherent bridge measures a horizontal distance of 140 ft to the design. It was amazing to see reinforcing steel (43 m) with the supporting arches above built on a mesh exposed in a hydrodemolition test area in the 160 ft (49 m) radius. The remaining 210 ft (64 m) same condition as when it was placed on the bridge of the center span are supported from below by the 90 years earlier. Even with all the modern shotcreting continuation of the arches on a 306 ft (93 m) radius. tools we have today, duplicating the quality of The box beam arches start with a section of 10 ft the shotcrete work on this bridge would be a (3 m) deep at the base, reducing to a 6 ft (1.8 m) major challenge. depth at the top with the width remaining the same The shotcrete covering had caused many a bridge expert to be deceived into thinking this was a struc- A unique feature of the original project was the encasement of the ture made entirely of concrete. Originally placed steel structure in what was then called “gunite” to protect it from the using the dry-mix method nearly a century before, emissions of the paper mill located close-by. “The guniting was done the protective concrete would need to be removed under subcontract by Lanning & Hoggan and was directly supervised and replaced to the original lines and grades. One by A.C. Forrester, Civil Engineer. The outfit used was the N-1 type cement of the first questions to contemplate was: Should it gun of the Cement Gun Co., Inc., and the necessary auxiliary equipment… be done wet or dry? Should it be both? Today’s The work required 40,000 square feet of 2 inch guniting on the steel ribs; shotcrete technology offers efficient site batching 1200 square feet of 6 inch gunite for the web on the underside of the of material in small amounts, both wet and dry; arch; 800 square feet of 4 inches thick; 1200 square feet of 3 inches thick, state-of-the-art batch plants and testing facilities also and 2800 square feet varying from 6 inches down to 2.” allow ready-mix producers to perform various adjustments and quality control that simply was not W.A. Scott, Engineering World (December 1922) available 90 years ago. The project has areas that 26 Shotcrete • Winter 2014


2014WinShotcreteEMag
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