Interestingly enough, in somewhat typical PENNDOT fashion, there is a disagreement about the significance of the Birmingham Bridge.
HAER describes the bridge’s significance: http://lcweb2.loc.gov/cgi-bin/ampage?collId=pphhdatapage&fil...
“This single span pin-connected Pratt through-truss is unique for a Pratt truss in that the portals contain hip verticals that carry compressive stresses (hip verticals for the standard Pratt truss type carry tensile stresses only).”
On the flip side, PENNDOT notes in the PA Historical Bridge inventory, “The lower panel point has been changed significantly with the original hanger replaced with riveted connections to plates attached to the verticals. The floor beams appear to have been replaced when the connection was changed. The bridge is an altered example of a type and design that is well represented in the region and state. It is not historically or technologically significant because of the alteration to the lower panel points.”
Whatever camp you sit on you can no doubt appreciate the beauty and uniqueness of the portals at both ends of the bridge which feature decorative panels containing clover-leaf cutouts in the web section of the lateral bracing.
I should point out that the name of the road the bridge carries is called “Irish Flats” so one can assume the clover leaf cut-outs on the top chord might be related. Four leaf clovers represent good luck which might be why this forunate bridge is still standing.
Birmingham Bridge rests on abutments with wingwalls made of cut-stone sandstone also known as ashlar.
The bridge consists of compression members of steel channel sections and riveted lacing bars; and tension members of forged steel eyebars. A diagonal compression member extends from the junction of the lower chord and hip vertical to the main portal member. Steel I-beam floor beams and strings support the 3” thick plank on steel stringers and beams wooden deck.
Based on the inscription on the masonry abutments the bridge was built in 1898. This metal bridge replaced a wooden bridge constructed in 1852. When the through truss was built it included a pedestrian sidewalk on the downstream side but was later removed for reasons unknown.
Currently the bridge serves a single residence on the south side of the Little Juniata. The present owners are Blair and Huntingdon Counties (Blair County assumes actual responsibility for maintenance and both counties share cost equally). Bridge was sandblasted and painted in 1987.
Whether this bridge is considered significant is debatable, I for one am crossing my fingers in hopes that neither man nor Mother Nature remove this beautiful piece of work.