Rehabilitation is a major part of preservation. Rehabilitation keeps a historic bridge in active service, carrying vehicles, bicyclists, and pedestrians, while preserving Minnesota’s transportation heritage. It involves repair and upgrading of structural and mechanical components. Through periodic rehabilitation work, along with regular maintenance, a historic bridge can stay in active service for 100 years or more.
Historic bridge rehabilitation work must comply with federal requirements called the Secretary of the Interior’s Standards for the Treatment of Historic Properties—or the Secretary’s Standards. Compliance with the 10 Standards for Rehabilitation ensures that the bridge retains historic materials and appearance while meeting engineering and accessibility requirements.
Careful inspections, regular maintenance, and rehabilitation of Minnesota’s historic bridges is ongoing statewide. Below are several current and recent projects.
Currently in process
Minnesota bridge owners have more than 20 historic bridges in process for rehabilitation. Below are four current examples.
The 1942 Winona Bridge (Bridge 5900) is undergoing full rehabilitation between 2017 and 2019. To accommodate increased traffic between Minnesota and Wisconsin, a second and parallel Mississippi River bridge was built just upstream in 2016. At that point, all traffic was temporarily shifted to the new bridge and the historic bridge was closed for rehabilitation.
The three, steel, cantilevered through-truss spans across the river—the bridge’s most significant feature—are undergoing extensive steel repairs. When completed, these main spans will retain all historic features and character. The steel deck-truss approach spans on each end of the through-trusses, are being removed and replaced with identical trusses using modern steel materials. The concrete approach spans on the south side of the river are being removed and replaced with new prestressed concrete spans in a modern design that will reflect the materials and appearance of the original spans. At each end of the rehabilitated bridge, the abutments of the historic and the new will be side-by-side in a complimentary arrangement, with any historic features replicated in the reconstructed abutments.
Videos of the Winona Bridge (Bridge 5900).
Broadway Bridge (Bridge 4930) carries State Highway 99 over the Minnesota River at Saint Peter in Nicollet County. This two-span steel through-truss bridge was completed in 1931. To accommodate river currents, the center pier between the two Pennsylvania-type truss spans was designed at an angle, or skewed, in relation to the bridge ends at the abutments. That skewed pier alignment required an unusual arrangement of trusses on the upstream and downstream sides of the bridge, contributing to the structure’s historic significance.
During the rehabilitation in 2017-2018, the steel trusses are being repaired and repainted in the historic color of dark green. The truss floorbeams are being strengthened to accommodate current loads. The concrete abutments and approaches are being repaired with surfaces carefully finished to match the original concrete. The historic lights on the bridge and approaches are being replicated. An extended embankment wall at the west side will protect the abutment foundation from erosion by the river, which changes depth constantly and is subject to seasonal flooding.
View a time-lapse of the bridge reconstruction (YouTube).
Bridge L5391 was built in 1909-1910 to carry Third Street over the Cannon River in Cannon Falls, Minnesota. It is the earliest of only three known examples of a Pennsylvania-type through-truss in the state. It is also significant as the design of an important engineer, Louis P. Wolff of Loweth & Wolff of St. Paul, and as the work of an important bridge builder, Alexander Y. Bayne of Minneapolis.
In 2016 the City of Cannon Falls received a Minnesota Historical and Cultural Heritage (Legacy) Grant to prepare engineering plans for rehabilitation. That process is underway.
As part of the rehabilitation, the modern timber deck will be replaced with a concrete deck similar to the original. The upper part of the abutment backwalls will be replaced to allow the bridge to expand and contract as originally intended.
The steel truss will receive repairs to floor beams, stringers, lateral bracing, and other components. The lattice-like railings will be repaired and will receive four new decorative endposts cast from the originals. The entire bridge will be repainted in a historically appropriate color.
The Kennedy Memorial Bridge was constructed in 1963, the year that President Kennedy was assassinated. It carries U.S. Highway 2 over the Red River of the North between East Grand Forks, Minnesota, and Grand Forks, North Dakota. The bridge established a new river crossing important to the economic development of the Grand Forks region. It is also significant for the exceptional length (279 feet) of its two Parker camelback-type trusses and for special engineering substructure features designed to accommodate the shifting banks of the Red River, while maintaining the stability of the bridge superstructure above.
The bridge is being rehabilitated in 2017-2018. One of its three river piers is being replaced with a similar pier that is one foot wider to facilitate future maintenance. The bridge's deteriorated concrete deck is being replaced. The new deck will be the same width as the original deck but will provide a new pedestrian-bike path separated from vehicles by a concrete barrier.
The railings' lower concrete parapets are being replaced with a similar design that meets modern safety standards. The original aluminum posts and rails were salvaged and will be reinstalled on top of the new parapets.
The truss floor beams are being strengthened with hidden shear studs to accommodate modern traffic loads. Truss support bearings are being repaired and a pin-and-hanger system that allows the bridge to move slightly is being replaced in-kind. The trusses are receiving minor repairs and will be repainted the original metallic color.
In the last 20 years, Minnesota bridge owners have rehabilitated more than 40 historic bridges. Below are several recently completed examples.
Completed in 2018
Beaver Bay Bridge (Bridge 9395), MnDOT state bridge
Bridge 9395 is a three-span, continuous, steel-girder structure. It carries State Highway 61 over the deep gorge of the Beaver River in the municipality of Beaver Bay, along Lake Superior’s north shore, in Lake County. It is significant as Minnesota’s first major highway bridge with welded girders. Standard practice before this was to “roll” hot, malleable steel into a girder or to rivet together steel plates and angles to “build up” a girder. Welding reduced the size and weight of girders, lowered fabrication time and cost, and decreased maintenance requirements. Bridge 9395 was built in two stages, one side in 1958 and the other in 1959, and was essentially two mirror-image structures separated lengthwise by a 1-inch gap. While sharing abutments and piers, these superstructures were not physically linked but effectively functioned as a single structure.
In 2017-2018, MnDOT rehabilitated Bridge 9395 to address deterioration of the deck and girders. The deck’s condition was so poor that it had to be completely replaced. This was an opportunity for MnDOT bridge engineers to consider reconfiguring the deck in light of today’s design standards and to accommodate a request by the Minnesota Department of Natural Resources for a pedestrian/bicycle lane for the new Gitchi-Gami State Trail. The engineers eliminated the 1-inch center gap and made the deck continuous, incorporating a protected 12-foot lane for the trail on the northwest side.
The original deck was flanked by concrete barriers topped by two-pipe aluminum railings. The barriers did not meet current safety requirements, but the aluminum railings were an important aspect of the bridge’s visual character. The contractor carefully removed the aluminum railings and kept them in a secure location while completing work on the new deck. MnDOT’s bridge engineers reviewed modern crash-tested barriers and selected the TL-4 design (known as the Nebraska Department of Roads Concrete Bridge Rail) as the closest in appearance to the historic barriers. These were installed on the new deck and the aluminum railings were mounted on top. The original bronze bridge plaques were attached to the new concrete end posts.
Beneath the deck, the original wind bracing was producing fatigue cracks in the girders. To stop the damage but retain this historic feature, splice plates with slotted holes were added to the bracing to allow movement. While the original design had too much wind bracing, the lateral bracing was insufficient, and six rows of new diaphragms had to be installed. Angle stiffeners for the diaphragms were bolted to the girders with hex-head bolts to differentiate them from original girder splice plates, which were riveted in place. All of these elements and the girders received fresh paint, which matched the historic color as closely as possible.
Completed in 2016
Through local efforts, the Dodd Ford Bridge, erected in 1901 in rural Blue Earth County near Amboy, was rehabilitated and reopened to traffic in 2016. The single-span steel Pratt-type truss is important as an example of the work of Lawrence Henry Johnson, an important early Minnesota bridge engineer.
The truss span was lifted off the deteriorated original abutments and placed on temporary supports while the contractor built new abutments. Then new steel I-beams were installed to span the Blue Earth River and support the historic truss, helping carry modern traffic loads, while maintaining the bridge’s historic character.
The rehabilitation resulted from a significant campaign my Blue Earth County citizens to promote preservation. In 2010, the Amboy Area Community Club received a Minnesota Historical & Cultural Grant (also known as a Legacy Grant) to assist in hiring a consultant to examine the costs and methods needed to restore and preserve the bridge
Constructed in 1920, the bridge was designed to span Long Meadow Lake, an overflow area of the Minnesota River just beyond the main river channel. It is significant for its five, steel, riveted, Camelback-type through-truss spans. The bridge had been closed to vehicular traffic since 1993 and closed to pedestrians in 2002. Its historic status required consideration of rehabilitation when the need for a trail crossing was identified at this location.
Beginning in 2015, the rehabilitation restored the bridge for pedestrian and bicycle use. Using an adjacent, temporary support system, the trusses were lifted off the piers and abutments so steel members could be repaired and restored to their historic appearance Truss members bent by previous vehicle collisions were heat-straightened. The timber deck was replaced with a concrete deck. New code-compliant railings were installed. Concrete abutments and piers were repaired. Graffiti was removed and steel was repainted. The rehabilitation work was completed in 2016.
Completed in 2015
Built in 1904 to allow pedestrians to cross over the streetcar track at the adjacent station, the Como Park Pedestrian Bridge is one of the oldest reinforced-concrete bridges in Minnesota. It was designed by noted Minneapolis bridge builder, William S. Hewett, and incorporates the patented Melan arch steel reinforcing system.
Before rehabilitation, the bridge had seriously deteriorated. The pedestrian railings had crumbled, forcing the city to close the bridge and the trail below, which had replaced the original streetcar track. Concrete on the arches had also deteriorated, exposing the internal Melan steel system. The federally funded rehabilitation project included removing unsound concrete, forming new concrete to restore the shape and details of the original bridge, placing a waterproof membrane below the deck to protect the arch from water damage, installing of a new deck that recreates the scoring pattern of the original deck, and custom-made decorative railing to match the original.
The restored bridge now provides a sound pedestrian crossing above and trail amenity below, and returns one of the iconic early twentieth century features of Como Park. The work was completed in 2015.
Completed in 2014
Built in 1933-1934, the Roosevelt Bridge in Austin, Minnesota, is significant for its unusual construction and as a representative of a Depression-era federal program. It was built with funding from the Civil Works Administration (CWA), one of the earliest New Deal programs and one of the briefest, lasting less than six months. The bridge carries Fourth Street Southeast (formerly River Street) over the Cedar River and is unusual in having stone masonry foundations supporting reinforced-concrete arches.
During the 2011-2014 rehabilitation, deteriorated stone masonry was replaced by stones matching the original size, color, and texture in areas of the abutments, pier, arch ring stones, spandrel wall, railing, and stringcourse. The replacement stone replicated the unusual undulating coursing pattern created by the original stone masons in the 1930s.
The rough-faced, random-coursed limestone railing was replaced with a new rail with a crash-tested reinforced concrete core and stone veneer. Bridge lights and pilasters were reconstructed using historical photographs and drawings as a reference.
In 2016, the American Council of Engineering Companies of Minnesota (ACEC/MN) recognized the rehabilitation of the Roosevelt Bridge with the Grand Award for Excellence in Engineering. The project was also recognized by the Preservation Alliance of Minnesota with an Honor Award in 2015.