Gerloff road bridge (1/4)
Nestled among the trees, on an out-of-the-way stretch of Gerloff road (Lower Frederick Twp, PA) stands an interesting bridge that managed to avoid the wrecking ball. Built in 1888 by the Phoenix bridge company the structure was deemed unsafe for existing traffic by 1970. It wasn't immediately demolished, allowing supporters time to get it listed on the National Regiister of Historic Places in 1988. This wouldn't prevent removing an unsafe structure, but did help delay it while alternatives were explored. An image at bridgehunter.com shows the overgrown structure circa 1998. Rehabilitation involved engineering a steel-tied arch to bear all of the weight of the deck, relieving stress without replacing the truss. Augmenting the structure could not be avoided, but the character of the original was essentially maintained. A contemporary arch bridge by the same company could be considered an inspiration for this design. A brief history of the structure is given in a special citation for historic preservation.
Elsewhere on Flickr:
cmh2315fl shows a similar truss bridge in Virginia that hasn't been modified with an arch.
hhistory08 shows the related walnut street bridge in Harrisburg, PA. This is the largest surviving example of this type of truss bridge, with 15 spans, and is now limited to pedestrian traffic.
Gerloff road bridge (1/4)
Nestled among the trees, on an out-of-the-way stretch of Gerloff road (Lower Frederick Twp, PA) stands an interesting bridge that managed to avoid the wrecking ball. Built in 1888 by the Phoenix bridge company the structure was deemed unsafe for existing traffic by 1970. It wasn't immediately demolished, allowing supporters time to get it listed on the National Regiister of Historic Places in 1988. This wouldn't prevent removing an unsafe structure, but did help delay it while alternatives were explored. An image at bridgehunter.com shows the overgrown structure circa 1998. Rehabilitation involved engineering a steel-tied arch to bear all of the weight of the deck, relieving stress without replacing the truss. Augmenting the structure could not be avoided, but the character of the original was essentially maintained. A contemporary arch bridge by the same company could be considered an inspiration for this design. A brief history of the structure is given in a special citation for historic preservation.
Elsewhere on Flickr:
cmh2315fl shows a similar truss bridge in Virginia that hasn't been modified with an arch.
hhistory08 shows the related walnut street bridge in Harrisburg, PA. This is the largest surviving example of this type of truss bridge, with 15 spans, and is now limited to pedestrian traffic.