Covered bridges are in essence truss beam bridges
with a covering to help protect the truss and prevent extra weight, such as
snow, from exerting pressure on the deck. The primary purpose of covering
the deck and trusses is to shield the bridge from snow and rain, and thereby
stave off decay and rot. Most of America's covered bridges were built
between 1825 and 1875, although the first one is credit to Timothy Palmer as
the "Permanent Bridge," built in 1805 across the Schuylkill River in
Pennsylvania. This is a sampling of bridges from Pennsylvania, New Jersey
and Vermont. For general information, the
Wikipedia article
is a good place to start. According to the Federal Highway
Administration
Covered Bridge Manual, less than 900 covered bridges remain out of some
14,000 that existed at one time across the United States. Another
resource is the
National Society for the Preservation of Covered Brdiges' website.
Mood's Bridge (right) in East Rockhill, Pennsylvania, was
destroyed by fire in June 2004.
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