|Bridge Name||Facility Carried / Feature Intersected||Location||Structure Type||Construction Date and Builder/Engineer|
4 3/4 Mile Road Bridge
||4 3/4 Mile Road Over Pine River||Rural: Midland County, Michigan||Metal 8 Panel Pin-Connected Pratt Through Truss, Fixed||1903 By Builder/Contractor: Tunnel City Bridge and Iron Works of Port Huron, MI|
|Main Span Length||Structure Length||Roadway Width||Main Spans||NBI Number|
|116 Feet (35.4 Meters)||120 Feet (36.6 Meters)||15 Feet (4.6 Meters)||1||56314H00009B010|
This bridge is the only known bridge in existence built by the Tunnel City Bridge and Iron Works of Port Huron, Michigan. It is thus extremely important as what may be the last physical remnant of a little-known Michigan bridge company. In case you are curious why the company named themselves "Tunnel City" consider Port Huron's history during the period the bridge company was in operation. In 1891s, the first full-size sub-aqueous tunnel in North America was completed, running from Port Huron, MI and Sarnia, ON to serve trains. In 1903 when the 4 3/4 Mile Road Bridge was built, this key international tunnel would have been a major source of fame for Port Huron. Engineers would have possibly nicknamed Port Huron "Tunnel City" back then. Click here to visit HAER's page for this historic tunnel.
This bridge has been moved for a number of years, as MDOT's website mentions, and it took some searching to find who moved the bridge and where it moved. It turns out that a nearby resident, Jim Hyatt, moved the bridge to a nearby private drive and restored it. HistoricBridges.org is appreciative that this beautiful piece of Port Huron heritage was saved from the dumpster, which is where the Midland County Road Commission was going to put it.
Constructed in 1903, this bridge is a classic example of a pin connected Pratt through truss. The bridge is composed of eight panels yielding a 120 foot span. V-lacing is present on the vertical members, and lattice is present on the portal bracing. The original railings on the bridge are also lattice.
The bridge has been altered, most notably with extensive plate steel welded to bottom chord elements. In addition, the flooring system was also replaced, but with a wooden deck. Although MDOT's website mentions that the deck of the bridge was originally concrete, wood was a common surface for pin connected through truss bridges.
The unusual, simple plaque on the bridge which is composed of a thin plate with punched holes spelling out the bridge builder and date might at first glance appear to be not original. However there are a couple other bridge companies who created plaques of this type. After careful consideration, HistoricBridges.org believes the plaque to be original.
HistoricBridges.org thanks Jim Hyatt for allowing a visit and and photo-documentation of this important bridge, and also for choosing to save this historic bridge from certain doom!
Information and Findings From Michigan Historic Bridge Inventory
over the Pine River about a mile east of Gordonville, this medium-span
truss crosses the Pine River on the Gordonville Road. This pin-connected
Pratt through truss, extending 120 feet, is supported by concrete
abutments with angled wingwalls. The web members are built up from
rolled steel sections from the Cambria mills of Pennsylvania. They are
comprised as follows: upper chord and sloped end posts - two channels
with cover and batten plates; lower chord - 2 looped rectangular eyebars;
vertical - two channels with lacing (with two looped rectangular eyebars
at the hip); and diagonal - two rectangular eyebars. The guardrails are
lattice; The 12-foot-wide asphalt-covered concrete deck is supported by
I-beam stringers and floor beams, which are field-bolted to the
verticals. Other than the relatively recent installation of Armco
guardrails and turnbuckled tension rods at the hip verticals, the bridge
is unaltered. It is presently cloes to vehicular traffic.
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