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Riverside Avenue Bridge,
Bridge No. 3845
• Riverside Avenue over Metro North railroad
• Cast and wrought-iron Whipple through truss
• Length: 168'
• Built in 1871
• Francis C. Lowthrop, engineer
• Keystone Bridge Company, fabricator
Riverside Avenue Bridge is the only surviving bridge in Connecticut (and one of only about a dozen in the entire country) that has major structural members made of cast iron. Cast iron was widely used in trusses up until the early 1870s. Because it breaks under tension (bending or stretching forces), cast iron is only suitable for compression members, such as the hollow tubes that make up the top chord and verticals of this bridge. In contrast, wrought iron, which is produced by rolling hot metal under pressure, could be used either in tension or in compression. As the American iron industry matured, wrought iron became more widely available, and after several disasters involving improperly engineered bridges that were part cast-iron, wrought iron totally superceded the earlier material for use in bridges.
Riverside Avenue Bridge incorporates several other archaic features. The form of the bridge is based on a truss shown in Squire Whipple's pioneering Treatise on Bridge building, published in 1847. The Whipple truss, which has diagonal tension members running across two panels, was popular with early engineers. The bridge also illustrates the specialized connections characteristic of early trusses. The cast-iron lower-chord junction boxes and the ribbed blocks through which the diagonal rods pass were two improvements on the Whipple truss patented by engineer Francis C. Lowthorp.
Riverside Avenue Bridge was originally part of a multi-span railroad bridge crossing the Housatonic River. When the New Haven Railroad replaced the bridge in 1888, it salvaged several spans for re-use as highway overpasses. Riverside Avenue Bridge was erected in its present location about 1895. It was listed on the National Register of Historic Places in 1977.