10 Mile Road Bridge

Information and Findings From Michigan Historic Bridge Inventory

Narrative Description

This small-scale pony truss carries Parker Road over the Charlotte River about 6.5 miles east of Dafter. The bridge is a 50-foot, three-panel, rigid-connected Warren pony truss, with web members made up of back-to-back pairs of steel angles. I-beam floor beams are field-bolted to the verticals, and support the concrete deck. The webs are braced by steel-angle outriders bolted to the verticals. The truss is carried by concrete full-height abutments with angled wingwalls. The truss has more recently been braced by building a timber pile pier at mid-span. This is the only serious structural alteration it has undergone.

Before the standardization of truss bridge design by the state highway department, county and township road commissions in Michigan sometimes economized on bridge construction by substituting "two-angle" truss superstructures for the more traditional configurations. Instead of built-up box beams for the upper chord and end posts, these lighter structures used back-to-back angles, substantially decreasing the superstructural weight and, with cost predicated by the amount of steel in the bridge, reducing its cost.

Statement of Significance

Two-angle trusses were fabricated with both Pratt and Warren web configurations, invariably with rigid connections. The Parker Road Bridge in Chippewa County exemplifies this construction trend. A cast iron plate on its end post identifies its fabricator as the Minneapolis Bridge Company. Built in 1914, apparently for the Bruce Township Board, it is the only such two-angle truss in Michigan that has been definitively dated. As such it is distinguished as the best-documented representative of this relatively common pony truss subtype.