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D Street Bridge

D Street Bridge

Primary Photographer(s): Nathan Holth

Bridge Documented: April 8, 2013

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Key Facts

Facility Carried / Feature Intersected
D Street Over Petaluma River
Petaluma: Sonoma County, California: United States
Construction Date and Builder / Engineer
1933 By Builder/Contractor: Unknown and Engineer/Design: Leon Hagop Nishkian of San Francisco, California

Technical Facts

Rehabilitation Date
Main Span Length
80 Feet (24.38 Meters)
Structure Length
205 Feet (62.48 Meters)
Roadway Width
32.2 Feet (9.81 Meters)
1 Main Span(s)
NBI Number

Historic Significance Rating (HSR)

Bridge Documentation

View Archived National Bridge Inventory Report - Has Additional Details and Evaluation

Dating to 1933, this bridge is a rare example of a single leaf highway bascule bridge. It features a truss superstructure. Like most bascule bridges, the depth of the truss is variable, being greater at the counterweight end of the bridge. However, unlike many truss bascule bridges, the top chord is not polygonal or curved, and instead follows the same angle throughout its length. This gives the overall truss an unusual triangular appearance. The bascule is a fixed trunnion design with the counterweight under the roadway in a tail pit. Unusual among fixed trunnion bascules with under-deck counterweights built during this period, the operating rack for the bridge is on the exterior of truss, facing outward, away from the bridge. In other words, the rack is out in the open and easily visible. Compare this to the city of Chicago which specialized in building fixed trunnion bascule bridges. Within ten years of building bridges of this type, Chicago quickly switched from an outward facing rack to placing the rack inward facing behind the end of the truss. This concealed the rack within the truss web, making the bridge more aesthetically pleasing by making the mechanical element less visible. The consulting engineer who designed this bridge, Leon H. Nishkian definitely had a preference for the outward facing rack however. Visit the 3rd Street Bridge page to learn more about Leon H. Nishkian and to see another bascule bridge he designed with outward facing operating racks.



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