Question for the Forum: Parker or Not?

Side view of the bridge. Photos courtesy of Nathan Holth.

In connection with the series on the dire state of Massachusetts’ historic bridges and plans to demolish and replace them, here is a unique bridge that is worth mentioning. Located over the Powwow River in Amesbury, the Main Street Bridge is known as one of the smallest swing bridges that still exists in the country, albeit no longer functional. Built in 1891 by the Boston Bridge Works, the green-colored bridge is 110 feet long with a vertical clearance of between 10 and 11 feet. The roadway width is 23 feet. The bridge was rehabilitated in 1998 by replacing the original flooring with steel stringers with a concrete decking, thus rendering the truss structure as non-functional but more of a decoration. Yet, the bridge is considered historical to state standards and is still being used today by residents.

Transversal view

 

The unique part of the bridge is the truss design, for despite its riveted connections, the truss has a polygonal top chord with the center (swing) panel having an A-frame in the middle. Even weirder is the fact that the outer panels have the characteristics of a Parker design, whereas everything else seems to be a hybrid of a Warren and Thacher design. This creates a problem as to determine what truss type this bridge really is. Was there a Parker variant of the Thacher truss that was patented after 1884 (the year the actual Thacher truss was introduced), or was there a totally different truss type that was experimented by a bridge engineer wanting to leave a mark in his legacy? It is unclear how to determine the bridge type with this bridge, for it is not necessarily an outright Parker, nor a Thacher, nor a Warren. What do you think this bridge is?

More about this bridge via HistoricBridges.org, where more pictures and information on its history can be found here.

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