There are two reasons that I chose to write about the Wisconsin-Michigan Railroad Bridge over the Menominee River between the two states.
The first reason is that it’s a good example of the small truss bridges that were built everywhere in the US in the late nineteenth and early twentieth centuries. Wagner, Wisconsin, and Lake, Michigan, are small towns that have always been considered to be out of the way. The bridge was built in 1894 for the Wisconsin & Michigan Railway Company as part of a route carrying lumber from logging operations to the north to ports on Lake Michigan for shipment to Chicago. As lumbering died off, so did traffic on that railroad, leading to the bridge being converted to road use in 1938. It was demolished in 1991, shortly after the HAER survey.
As the HAER report discusses in detail, it’s not possible to separate discussion of this bridge, the second on the site, from the first bridge, completed in March 1894 after only a few months construction, and badly damaged by a log-jam on the river in April. The second bridge was begun in July and opened in November. The new bridge removed one of the two river piers of the old design to reduce the likelihood of another log-jam, resulting in two spans of unequal length; there’s no way to tell if that design change is the reason that there was not a similar problem, or if the general decrease in loggers floating lumber on the river was the reason.
The bridge is a through Pratt truss design, with all the standard elements: pin connections, eye-bar tension members, built-up-box compression members, portal bracing at the truss ends and wind bracing between. I personally like the detail that the portal bracing consists of small lattice trusses, but that’s a pretty minor detail.
The speed with which the second bridge was built shows how little unique design there was in a typical bridge like this. The design of a truss for known railroad loading had been performed and there was no need to redo it; wind-bracing design was, then, very simple and there was no need to redo that. Given any ordinary span, a bridge company could pull out a design and create the drawings without having to start from scratch.
The HAER report has an interesting suggestion about why this bridge was in service as long as it was – about 97 years from construction to demolition, with no period of abandonment. It was built by a small and poor railroad, that couldn’t afford new engines often, so the railroad loads on the bridge didn’t increase the way they might have if it was on a main line. And then when converted to road use, it was lightly used because of the small amount of traffic at its out-of-the-way rural location.
The second reason for selecting this bridge is that I much prefer cold weather to hot weather, so that by this time of year the heat is wearing on me, and the pictures of the bridge surrounded by ice and snow were a great relief. The pictures were taken in March 1989, in case anyone was wondering what early spring is like in that part of the US.
Permalink