Whipple Truss Bridge Structure
(used on the 1883 Blair Crossing Railroad Bridge built by George S. Morison)
“Comprised of three 330-foot Whipple trusses supported 50 feet above the high water by massive stone piers, the Blair Bridge took a year to build and cost almost $1.3 million: $400,000 of which was spent on shore rectification. — completed Oct 1883
“Morison’s Whipple trusses at Blair had been replaced in 1924 with Parker trusses fabricated by the American Bridge Company in New York.” ALMBridge page 24
About Squire Whipple & his Bridge Design (source)
The Whipple truss was developed by Squire Whipple as stronger version of the Pratt truss. Patented in 1847, it was also known as the “Double-intersection Pratt” because the diagonal tension members cross two panels, while those on the Pratt cross one. The Indiana Historical Bureau notes one bridge as being a “Triple Whipple” — possibly the only one — built with the thought that if two are better than one, three must be stronger yet.
The Whipple truss was most commonly used in the trapezoidal form — straight top and bottom chords — although bowstring Whipple trusses were also built.
The Whipple truss gained immediate popularity with the railroads as it was stronger and more rigid than the Pratt. It was less common for highway use, but a few wrought iron examples survive. They were usually built where the span required was longer than was practical with a Pratt truss. Further developments of the subdivided variations of the Pratt, including the Pennsylvania and Baltimore trusses, led to the decline of the Whipple truss.
Whipple Bridge at Sugar River north of Boonville, New York. (link)
Blair Historic Preservation Alliance | P.O. Box 94 | Blair, Nebraska 68008 | firstname.lastname@example.org