This bridge is unusual because its three main spans have polygonal top chords that are oriented in a manner that the three spans form a single arch shape, making the bridge look like a single continuous three-span truss. However, in reality the trusses are three simple spans. Mark Bozanich commented on www.bridgehunter.com that the Vernita Bridge was built with three simple trusses so that the center truss could be converted to a vertical lift span. There were plans at one time to build a dam downstream from Vernita and upstream from the Tri-Cities equipped with locks. Plans were abandoned now that the dam site is part of the Hanford Reach National Monument. Mark's comments seem to be supported by the physical configuration of the truss. Most notably, the piers for the center truss span are quite a bit wider than they need to be, suggesting that the piers were built to either completely or partially accommodate the towers that would be needed to make the bridge a vertical lift. Also, at the pier, the vertical end posts have empty bolt holes which could have been intended for attaching the lift tower and related materials.
The bridge is a late example of a metal truss bridge, and barely old enough to be considered historic. However, the bridge does stand out for its unusual false-continuous design. It also represents the end of the riveted truss era. Truss bridges built in the 60s like this bridge usually have details that show the decline in use of rivets and increase in the use of welds and bolts. What is unusual is that this bridge still used riveted connections, instead of bolted connections which are often found on 1960s bridges. In contrast, the built-up beams that compose the truss are welded, which is unusual since the built-up beams is one location where rivets are often still found on 1960s bridges.
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