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M-26: Eagle River Timber Bridge, 1991

A rather interesting and, for Michigan's state trunkline highway system, unique bridge sits on M-26 and spans the scenic Eagle River in the community of the same name in Keweenaw County, at the top of the Upper Peninsula. The following two articles have been reproduced from an internal Michigan Department of Transportation newsletter from the early 1990s.


The Eagle River Timber Bridge

Reprinted from the June 1991 issue of "Mates" (Issue No. 54), produced by the Michigan Department of Transportation.

A recent point of pride in the town of Eagle River, on Michigan's beautiful Keweenaw Peninsula, is a glue-laminated timber bridge which carries M 26 over the Eagle River. Aesthetically, the new bridge blends in well with the scenic Copper Country, and structurally it was designed to carry the same traffic loads as our State trunkline concrete and steel bridges.

The total length of the wooden bridge is just over 152 ft, and it stands 50 ft above the Eagle River. Supported by two, side-by-side arches spanning 74 and 79 ft, the bridge is primarily made of timber, with the connecting components fabricated of steel. An asphalt wearing course carries traffic across the wooden deck. All wood components were pressure treated with a preservative (pentacholorphenol in oil) an include the pedestrian railing and posts and deck support columns, wheel guards, beams and stringers, deck and the arches themselves. Enough lumber was used in the bridge to build three or four average sized houses.

Each of the two arches supporting the structure is actually made of two arched segments, joined at the top with a crown hinge, and measure 60 in. deep and 14 in. wide. The largest of the four segments is 42 ft from end-to-end, with a crown height of 25 ft, and weighs about 10,600 lb. The other three segments are 37 ft long, 18 ft to the crown, and weigh about 8,700 lb each. The base hinges that attach the arches to the concrete abutments and the two crown hinges, pivot on 4-in. diameter steel pins which are chrome plated to provide corrosion protection and lower friction resistance to any rotational movement of the arches.

All the steel in the structure (except the hinge pins) was hot-dipped galvanized, then covered with a tie-coat, an intermediate epoxy coating, and a brown urethane top coat. This coating system is designed to protect the steel for 30 years. Any timber members that were cut or drilled during construction were treated with two coats of copper naphthenate to protect the cut areas. The entire structure's wooden members will be recoated with preservative every three years, and at that time all bolts will be checked and retightened if necessary.

The timber bridge at Eagle River provides motorists with an aesthetically pleasing, functional structure. To one side is the vast expanse of Lake Superior and on the other side are splendid trees with a cascading waterfall. The bridge's appearance blends into the surrounding environment and was an idea choice for such a scenic location.

— Brian Ness

Eagle River Timber Bridge photo


1992 Member Bridge Award Competition

Reprinted from the November 1992 issue of "Mates" (Issue No. 69), produced by the Michigan Department of Transportation.

This article is intended to bring our readers up to date on recent activities relating to our unique timber arch bridge in Eagle River. As you may recall from our June 1991 MATES (Issue No. 54), this three-pin, twin-arch timber structure carries state trunkline M 26 over the Eagle River in the Keweenaw peninsula.

This structure is completely constructed of glue-laminated members fabricated from 147 MBF (thousand board feet) of Industrial Grade southern yellow pine, enough lumber to build three to four average size homes. The 152-ft long structure, with a clear roadway width of 38 ft, was designed according to the AASHTO Standard Specifications for Highway Bridges, HS-25 loading.

On August 26, 1992, the Eagle River timber bridge was officially entered in the 1992 Timber Bridge Design and Construction Award Competition sponsored by the National Forest Products Association, Special Task Group on Timber Bridges, and the U. S. Department of Agriculture, Forest Service. This modern wood bridge competition is open to all bridge owners (i.e., towns, cities, counties, and States), bridge architects, designers, contractors, and developers. Eligibility criteria for this competition required that all candidate bridges must have been open to traffic prior to January 1, 1992, and they must be located in the United States.

Awards will be presented in each of the following four categories:

  1. pedestrian/light vehicular bridges,
  2. vehicular bridges with main span over 40 ft,
  3. vehicular bridges with main span under 40 ft, and
  4. rehabilitation of existing bridges using wood components.

Our Eagle River structure was entered in the second award category, I:Vehicular Bridges with Main Span Over 40 Feet. Deadline for competition entry was September 30, 1992, after which a distinguished panel of judges, representing a wide diversity of timber bridge design expertise, will evaluate and select a 1st Place Award winner and Award of Merit winners in each of the four categories. Candidate bridges will be judged on the basis of their design innovation, visual appeal, cost effectiveness, and the use of sound engineering principles.

The competition is intended to highlight the innovative and efficient use of engineered wood products in helping to solve the problem of deteriorating bridges in the nation’s highway infrastructure: Award winners will be presented a plaque featuring a color photograph of the winning bridge along with the names of the designer, contractor, and owner. A separate plaque will be permanently affixed to the bridge itself for public display.

At the time this article went to press, the judges’ decisions in the competition were not yet known. We will publish any decision relative to our Eagle River bridge entry in a future MATES issue. If you are interested in learning more about the history, fabrication, and construction of the Eagle River timber bridge, contact me in the Research Laboratory at (517) 322-571.

— Glenn Bukoski



 

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