Thursday, February 4, 2021

1855,1876,1891,1990 Hennepin Bridges over West Channel of Mississippi River in Minneapolis, MN

1855-1876: (Bridge Hunter)
1876-1891: (Bridge Hunter)
1891-1989: (Bridge Hunter; HAER) It was demolished in 1989 to make room for the new bridge.
1990: (Bridge Hunter; John A. Weeks III; Satellite) It is six lanes wide. That requirement stopped preservation talks of the 1891 steel arch bridge.

The full name is Father Louis Hennepin Bridge.

The day after I discovered there was a suspension bridge in Cincinnati, OH, I also discovered a suspension bridge in Minneapolis while studying the Third Avenue Bridge.
John Weeks

I'm now switching to the chronological order of the bridges.

1855

This location was the site of what is believed to be the first permanent bridge over the Mississippi River. What was once the most important bridge over the Mississippi River is now the most elegant and stylish bridge to span the mighty river. The first bridge was built in 1854 and was opened on January 23, 1855. According to the state historical society, it was proclaimed as a link between the Atlantic and Pacific, and it was called the "Gateway to the West". The bridge was 620 feet long and 17 feet wide. It was a pure suspension bridge with tall wooden towers, wire suspension cables, a stone base, and cast iron anchors. [John Weeks]

Those cables would have been made with wrought iron instead of steel. I think that means that a lot of pounding of metal was done to make those cables.

1855 Bridge Hunter, research by Jake Bronder


1876

"The second bridge was another pure suspension bridge. It was 675 feet long and 32 feet wide, with towers that were slightly taller than the first bridge. Due to the importance of the river crossing, the second bridge was built parallel to the first bridge, and the first bridge was not removed until after the second bridge opened in 1876." [John Weeks]    Eads was built in 1874 using steel. But steel was bleeding edge technology back then. So these cables were also probably made with wrought iron.

1876 Bridge Hunter, research by Jake Bronder


1891

"Construction of the third bridge started in 1888 and was completed in 1891. This bridge was a steel arch bridge that was designed in-house by Minneapolis bridge engineers which included Frederick Cappelen, who designed many of the large concrete arch bridges over the river in the early 1900s. The third bridge was 1160 feet long, spanning the river in two 580 foot arches. The bridge had a 56 foot wide wooden roadway and two 12-foot wide sidewalks. The historical society reports that the wooden deck was replaced with a steel grid in 1954." [John Weeks]

The City Engineer proposed a stone arch bridge with three piers in the river to replace the 1876 bridge. But the citizens didn't want a plain old stone arch bridge. (I wonder if the twin-cities is the stone arch capital of the country. In most cities, a stone arch bridge would not be considered plain.) More significantly, the Milling Company that had built around the Upper Falls did not want three piers interfering with the flow of water to their intakes. The city council ignored public input and started on the stone arch bridge. But the Milling Company obtained a temporary injunction from the district court to stop all construction. The City Engineer was forced to join a committee to reevaluate the design. City Engineer Rinker estimated that a steel arch bridge with just one pier would be "much less than the stone arch bridge." [HAER-data] (Another example of engineers choosing designs that they have used in the past rather than learning lower-cost new designs happened during the design of the I-355 Bridge over the Des Plaines River.)

HAER MINN,27-MINAP,11--6

6. VIEW FROM NORTHWEST - Steel Arch Bridge, Hennepin Avenue spanning west channel of Mississippi River, Minneapolis, Hennepin County, MN


HAER MINN,27-MINAP,11--8

8. CENTER PIER, SOUTHWEST SIDE 


HAER MINN,27-MINAP,11--12

12. STEEL ARCHES, NORTH SIDE


HAER MINN,27-MINAP,11--16

16. CROWN HINGE CONNECTION AT ARCH CROWN

[I see the hinge in the two visible beams on the right in the middle where the beams taper to a point. But the two beams on the left have a uniform width across the center. HAER-data explains that the two halves were built by different companies and one used a three-hinge design whereas the other used a two-hinge design.]

1990

City Hall wanted a signature structure and paid three times more than what a UCEB (Ugly Concrete Eyesore Bridge) like the Plymouth Avenue Bridge would have cost. This bridge is actually two spans that share center towers. The towers are about 175' above water. [John Weeks]

Street View, looking Northeast

Note the observation platform that was built around the south side of the north tower. It is nice that city planners no longer ignore pedestrian and bike traffic like they used to. John has additional photos of  a bike ramp and a stairway that connects a river trail with the bridge walkway. He also has photos of a movie set that was constructed so that the bridge depicted a border crossing between Detroit and Windsor. He also has a couple of night photos showing the lighting.
John Weeks

The bridge uses a beam for the deck stiffening rather than a truss. The handrails are quite elaborate for a modern bridge. (I assume they are made with metal instead of plastic.)
John Weeks





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