Michigan's Bridges: Charlotte Highway Bridge at the Historic Bridge Park (2)

August 2011 (42.291 Degrees, -85.115 Degrees) Charlotte Highway Bridge

According to the Blair History Website a Pratt truss has parallel top and bottom chords and diagonal members in tension pointing down towards the middle of the span. A Howe truss is just the opposite with diagonal members in compression pointing towards the supports. A Whipple truss (patented in 1847 by Squire Whipple) is a variant of the Pratt truss with the diagonal elements crossing one or more vertical members (the diagonal members are usually plates or rods). The Charlotte Highway Bridge is a Whipple truss. The Windsor Bridges over the River Avon in England that we studied on March 6, 2010 are bowstring Whipple trusses.

According the website, the Whipple truss was stiffer and stronger than the Pratt, which made them popular with the railroad companies, until they were supplanted by further variants of the truss design. The Pratt truss was used for spans up to 250 ft in length and the Whipple trusses on the 1883 Blair Crossing Railroad Bridge were 330 ft long. 

Michigan's Bridges: Charlotte Highway Bridge at the Historic Bridge Park (2) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.