Bridge 2796 on 10th Avenue over Mississippi River
Bridge number: 2796
Year built: 1926-1929
Engineer: Kristoffer Olsen Oustad
Contractor: City of Minneapolis
Overall length: 2,174.9 feet
Overall width: 68.1 feet
Adapted from the National Register of Historic Places nomination form prepared by Robert M. Frame III. The Cedar Avenue Bridge was listed in the National Register of Historic Places in 1989.
The Cedar Avenue Bridge is located less than one mile east of the city hall and downtown loop, and a few blocks north of the west bank campus of the University of Minnesota, in Minneapolis, Minnesota. It connects Cedar Avenue on the south, across the Mississippi, with Tenth Avenue Southeast on the north. When it was built it also linked with Johnson Street Southeast on the north. The original arrangement of streets in the vicinity of the Cedar Avenue Bridge was disrupted by the alignment of Interstate 35W, which was constructed in the 1960s-1970s. Parallel to, and a short distance from, the Cedar Avenue Bridge on the upstream is the Interstate 35W bridge, erected in 1967. A short distance downstream is the Northern Pacific Railroad bridge, which was erected in 1884-1885 and thoroughly remodeled in ca. 1917.
Aligned on a northeast-southwest axis, the Cedar Avenue Bridge is a reinforced concrete, open-spandrel, two-rib, continuous-arch bridge, with an overall structure length of 2,174.9 feet. In the original, continuous-arch unit, it has two main spans of 265.5 feet each that cross the river channels and five flanking spans of 93 feet each, two on the northeast end and three on the southwest end. The flanking spans are aligned so as to give the bridge an S-curve in plan, with the three southwest spans on a curve of 5 degrees 41 minutes. The two northeast spans are on a curve of 5 degrees 18 minutes. Thirteen minor, precast-concrete-beam, approach spans were added in 1971-76, replacing a series of I-beam approach spans. All the arch spans have two ribs 12 feet wide and 24 feet apart in the clear, with a thickness for the main spans of 3.5 feet at the crown and 7.5 feet at the haunches. A three-center radius of 154 feet and 48.5 feet is used for the intrados and a single radius of 167.5 feet for the extrados. Each rib of the main spans is reinforced with five steel ribs 31.5 inches deep at the crown, having chords composed of pairs of angles with smaller angles for the web members. In the 93-foot spans, each rib is reinforced with sixteen longitudinal bars at top and bottom, tied together with loop bars. Footings for the three river piers are 30 feet by 54 feet. At the east and center piers, they rest on the sandstone bedrock at 11.5 feet and 22.5 feet below low water, while the west pier footings are supported on 180 piles, 32 feet to 42 feet long, driven into a gravel formation. The main spans have a rise of 90.5 feet, with the crown about 110 feet above low water.
Transverse spandrel walls are practically the full width of the arch ribs and spaced 13.3 inches center to center in the main spans. Transverse spandrel walls are 12 feet in the flanking spans support floor beams that carry the deck and are cantilevered to support the sidewalks. With the 1971-1976 redecking of the bridge, the deck width is 68.1 feet, carrying a 55.5-foot roadway, with a sidewalk on one side and a bikeway on the other.
When built, the bridge had a simple, relatively unornamented surface taking its beauty from the elegant line, form and proportion of the engineering itself. A July 10, 1930, description in the Engineering News-Record stated that "Except for the rubbing of [the concrete] railing to a smooth finish no special treatment was given to the exposed concrete surfaces for the sake of appearance." Simple inset, vertical panels of mild Classical Revival/Art Deco style were the only stylistic additions to the piers and these were retained in the remodeling.
The Cedar Avenue Bridge is historically significant as an excellent example of the monumental urban, continuous-rib-arch, reinforced concrete bridges constructed in the Twin Cities to span the high and scenic Mississippi River bluffs during the early automobile age. As such, it is one of the major extant examples of the second and "golden age" of reinforced concrete, arch-bridge design and construction in Minnesota. The first era was the 1880s, metal-bridge era. Engineering historian Kenneth Biork points to a series of factors that created the special bridges of the great reinforced concrete bridge era between World War I and World War II in the Twin Cities. The common transportation obstacle of the high-bluffed Mississippi River, the coming of the automobile and the truck and the converging of many highways into the cities placed a heavy burden on the early bridges. As a result, innovative bridges were designed recognizing the need for greater concentrated loadings needed to support greater volumes of traffic and streetcar tracks. Since the bridges often linked two cities, the need for joint, two-city planning and financing had to be developed in some cases.
When completed in 1929, the Cedar Avenue Bridge was the longest and highest of the monumental concrete-arch bridges erected in Minneapolis and a significant engineering accomplishment. With an as-built overall structure length of 2,921 feet, it was 698 feet longer than its closest rival, the Third Avenue Bridge. With a vertical clearance of 110 feet, it was 10 feet higher than the Cappelen Memorial (Franklin Avenue) Bridge. Even with the various remodelings that all the Twin Cities bridges have undergone since construction, it is still the longest of the historic, pre-1945 reinforced concrete, continuous-arch bridges. To find a longer pre-1945 structure in the Twin Cities metropolitan area, it is necessary to look to the record-breaking, 4119-foot Fort Snelling-Mendota Bridge, which was the world's longest reinforced concrete, continuous-arch bridge when built.
An additional point of technological significance is that the Cedar Avenue Bridge was one of the first constructed using water-cement ratio specifications for proportioning concrete. Design stresses ranged from a low 2000 pse in the foundations to a high of 3000 pse in the arch ribs. Test cylinders taken from the mixing plant verified that the new procedure was successful in addition to being more economical.
The Cedar Avenue Bridge is the crowning achievement of Kristoffer Olsen Oustad, who is significant as one of four, major, innovative and influential Norwegian-American engineers that were involved in the design of the great bridges of the Twin Cities. The others are Martin Sigvart Grytbak, Andreas W. Munster and Frederick William Cappelen. Educated at Trondhjem's Technical College in 1882, Oustad joined the Minneapolis city engineer's office in 1883, becoming municipal bridge engineer in 1893. When the Cedar Avenue Bridge was completed in 1929, Oustad retired, 46 years after he began. He had assisted famed Norwegian-American engineer Frederick William Cappelen in the design of two earlier concrete arch-bridge landmarks, the Third Avenue Bridge and the Cappelen Memorial (Franklin Avenue) Bridge. Oustad completed the Cappelen Memorial Bridge when Cappelen died. The Cedar Avenue Bridge, however, was Oustad's work, assisted by Frederick T. Paul, assistant bridge engineer, under the direction of N.W. Elsberg, city engineer.
As the first bridge ever built at this location, the Cedar Avenue Bridge was planned to fill several pressing transportation needs in Minneapolis. In general, it provided relief from downtown-loop congestion caused by limited river crossings and increased north-south traffic, including tourist traffic utilizing "the new Duluth Highway." On the north and east were several major industrial districts, including the Northwest Terminal, in the vicinity of Stinson Boulevard and East Hennepin Avenue, and the milling and terminal-elevator concentration in the Midway, north of University Avenue. The bridge provided these industrial areas with direct access to a proposed $300,000 modernization of the river/rail terminal on the south and west. In addition, the federal government was scheduled to operate a fleet of barges on the Mississippi.
Initial federal authorization for the bridge was received in 1924, with the federal plan approval in 1926. North approach spans were constructed 1923-1926. Construction bids were opened in 1926 and the lowest bid, $891,000, was submitted by the City of Minneapolis, acting through the City Engineer. Work commenced on the bridge in June, 1926, using day labor. Construction was completed in October, 1929. The bridge was officially dedicated in September, 1929.
The bridge was redecked and new approach spans added in 1972-1976. The alterations do not substantially reduce the structure's overall integrity since the original seven arch structures and spandrels, incorporating all of the bridge's significant engineering elements, were repaired and restored. The replaced I-beam approach spans were not an integral part of the significant reinforced concrete superstructure and were not even discussed in an engineering review of the bridge in 1930.