OIL CITY, PA- Between through truss bridges which have an overhead chord and a deck truss, where the trusses are underneath the roadway, we have the half-through truss design. This consists of a truss bridge, whose roadway is wedged right in the middle of the truss itself. This means the truss can be seen both when driving by car on the road or boating underneath. Only a handful of These half-through truss bridges were constructed between 1880 and 1940, of which seven existed, including two with overhead bracings that cover the roadway, resembling a true through truss bridge.
Since October 4th of the year, that number has been reduced to one. The Hunter Station Bridge, a three-span Pratt half-through truss Bridge spanning the Allegheny River at US Highway 62 between Oil City and Lighthouse Island in Forrest County was dropped with explosives last week, two months after ist replacement span was open to traffic. The 1050-foot Long span was built in 1934 by P.I. Cox Construction Company featured a 30° skewed overhead chord with X-laced portal bracings encased in a C-beam form that can be seen as a beam portal upon entering the bridge. The strut bracings are all X-laced and uncovered. The roadway is wedged between the riveted trusses, even though a sidewalk existed on one side. The structure was listed as eligible for the National Register of Historic Places, but it was not enough for the it to be saved, for years of neglect with rusted trusses and damages to concrete and steel railings led to PennDOT to replace the structure with the new span. Construction started last year and traffic shifted onto the new bridge in July, when it was completed to traffic.
With the Hunter Station Bridge now gone, only six half-through truss bridges exist in the US, 10 worldwide. This includes the Purdon Bridge near Nevada City, California, the last of ist Kind with an overhead chord. The pin-connected Pratt design, built in 1889 by Cotton Brothers Construction in Oakland is listed on the National Register and still in use today. Other half-through trusses in the US without the overhead trusses include the Nemadji Railroad Bridge in Wisconsin, Dearborn Bridge in Montana, Hadley Bow in New York and High Bridge in Indiana. It is unknown whether another half-through truss bridge in South Carolina exists according to information from bridgehunter.com.
Link: http://historicbridges.org/bridges/browser/?bridgebrowser=truss/hunter/
