Mystery Bridge Nr. 60: Unusual Howe Lattice Truss Bridges

Photos taken by MnDOT
Photos taken by MnDOT

Our 60th mystery bridge ironically runs parallel to a highway bearing the same number running through another Minnesota county- Blue Earth! The exceptions though are the following:

  • These are two unusual bridges that have long since been recycled for reuse- at least three times over the course of 35+ years, and
  • They are located in the southern part of the county, whereas the major expressway is in the northern half, where Mankato, Lake Crystal and Janesville are located.

The bridges are similar in length and width, but the designs are rather strange. They both feature a Howe truss design but resembling a Howe Lattice portal bracing of a through truss bridge, like these bridges:

Kelly Lane Bridge  This and the following photos courtesy of Craig Guttau, used with permission
Kelly Lane Bridge in Harrison County, Iowa. Photo  courtesy of Craig Guttau, used with permission
Salisbury Bridge in Meeker County. Photo taken in December 2010
Salisbury Bridge in Meeker County. Photo taken in December 2010

The engineer behind the construction of the bridges- each being built in 1911 shortly before the standardized truss designs were implemented- used light steel, supported by thick gusset plates as seen in the pictures below:

5445b

5645b

Also noticeable were the diagonal outer beams supporting the trusses  to ensure that the trusses remained stable when the cars crossed them. This unusual contraption leads the historian to believe that despite the building date being 1911, that the truss bridges consisted of parts from an even bigger truss bridge or larger building that had existed. It was not rare to have truss bridges constructed using steel parts from old buildings, as is seen today with the bowstring arch bridges at Kent Park in Johnson County as well as the ones built in 1945-6 in Crawford County– both in Iowa. All of them are still in service serving light weight traffic. This is even more noticeable as the connections seemed to be welded together instead of pin-connected or even riveted.

Sadly, both bridges are long gone. As you can see in the links, one bridge over the slough portion of the Maple River south of Mapleton was replaced in 1978, the other east of Amboy spanning Rice Creekwas replaced in 1980. Still a lot of mysteries are left over from the bridges- namely who built the bridges and how were they built. Even more curious is whether the construction date of 1911 for both bridges were given by the bridge inventory or if they were relocated or reassembled at an unknown time.

Any ideas? Put them here in the contact form and we’ll add them to the database in the bridgehunter.com website, where the bridges are posted. More Blue Earth County bridges will come later on, as the numbers are huge and many bridges have a history of their own.

Happy Bridgehunting and researching! 🙂

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