The bridge was designed by the Oregon State Highway Department under the guidance of State Bridge Engineer Conde B. McCullough and was constructed by contractor J.F. Johnston.
The South Fork Yamhill River Bridge is unique in regards to other reinforced concrete deck girder structures throughout Oregon for the fact that it was built directly on the abutments and pier of an old timber pony truss bridge.
The original bridge built at this location in 1920 was a two span timber pony truss bridge that totaled 101-feet in length. The original pony truss spans were 50-feet long and were of the half-hip Pratt truss configuration. The bottom chord of the truss was made up of 10” X 10” sawn timbers and the top chords were made from 8” X 8” timbers. The connections were made by notching and bolting the members together.
The current reinforced concrete deck girder structure built in 1929 was designed to sit directly on the middle pier and the west abutment. The east abutment was originally constructed of timber members and was reconstructed during the replacement project with reinforced concrete.
The new structure consists of two 50-foot long reinforced concrete deck girder spans that have limited architectural treatments. The only notable design detailing is the standard arched opening railing that was used by the Oregon State Highway Department on bridges in the 1920’s as well as the curved elbow brackets utilized under the overhang soffit.
Both the 1920 and 1929 bridges were designed by the Oregon State Highway Department under the supervision of State Bridge Engineer Conde B. McCullough. It is speculated the extremely wet environment of Oregon’s Coast Range combined with the growing vehicular loads of the 1920’s led to the replacement of the original bridge after only nine years of service.
Oregon Department of Transportation, Bridge Section, Bridge Drawings