From on the road, this bridge appears to look like a traditionally composed polygonal Warren pony truss with riveted connections and extensive use of rolled beams in the truss web. However, upon closer examination, the bottom chord turns out to have pinned connections. Everything else on the bridge is riveted. This hybrid use of riveted and pinned connections is extremely rare and although the Historic Bridge Inventory did not initially agree with this assessment, they later revised the inventory to find this bridge eligible. Another two-span example of this same design was demolished, making the Senn Bridge even more rare. Now this bridge is example putting the existence of any examples of this rare design in Pennsylvania in peril.
Information and Findings From Pennsylvania's Historic Bridge Inventory
Discussion of Bridge
The one span, 91'-long Warren with a polygonal top chord pony truss bridge is supported on concrete abutments. It was built in 1929. The upper and lower chords are rolled I section, and they are connected by rivets at the gusset plates except for the interior bars of the lower chords that are pinned rather than riveted. The gusset plates were used to connect the heavy, wide diagonals to the lower chord. The detail is unusual, but it is not historically or technologically significant. Use of rolled section for pony truss members dates to 1919, so this is not an early example.
The pinned lower chord is a technologically significant detail.
Discussion of Surrounding Area
The bridge carries a 2 lane road over a stream in a sparsely developed, forested and agricultural setting with some 20th century residential development visible from the bridge. The area does not appear to have historic district potential.
Bridge Considered Historic By Survey: Initially No, Revised To Yes.
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