The Veterans Memorial Bridge (Image)
Isambard Kingdom Brunel’s celebrated bridges—such as the Windsor Railway Bridge—are sometimes referred to as the earliest built examples of tied-arch bridges. But while Brunel’s wrought iron structures were groundbreaking and remain engineering landmarks, their primary innovation lies in their truss configurations, not in the development of the tied-arch system.
Images describe true-arch (top) and tied-arch (bottom) behavior. Differences in compression and tension are highlighted in blue and green.
The bowstring truss—often conflated with the tied-arch—actually has a more modest and distinctly American origin. Squire Whipple, an American engineer, is credited with inventing and patenting the bowstring truss bridge in 1841. Whipple’s design was the first to apply scientific analysis to bridge construction, using cast iron for compression members and wrought iron for tension, and incorporating a “string” (tie) to resist the outward thrust of the arch. His approach not only advanced structural understanding but also enabled rapid, economical bridge construction for projects such as the Erie Canal. Hundreds of Whipple’s bowstring truss bridges were built across the United States, and his work set the standard for canal and early railway crossings…