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A covered bridge is a timber-truss bridge with a roof, decking, and siding, which in most covered bridges create an almost complete enclosure. [1] The purpose of the covering is to protect the wooden structural members from the weather.
The design principle behind the Burr arch truss is that the arch should be capable of bearing the entire load on the bridge while the truss keeps the bridge rigid. Even though the kingpost truss alone is capable of bearing a load, this was done because it is impossible to evenly balance a dynamic load crossing the bridge between the two parts. [5]
Smith's company used many variations of this pattern in the wooden covered bridges it built. While most all of the bridges built in the 19th century in the Jackson County, Ohio, area used the Smith truss design, the Johnson Road Covered Bridge is the last known surviving example in the state. [33]
A simple lattice truss will transform the applied loads into a thrust, as the bridge will tend to change length under load. This is resisted by pinning the lattice members to the top and bottom chords, which are more substantial than the lattice members, but which may also be fabricated from relatively small elements rather than large beams.
This 86.5-foot-long (26.4 m), 18.66-foot-wide (5.69 m), Howe truss bridge was built in 1855. It was renovated by the Works Progress Administration in 1939, and by the city of Philadelphia in 2000. [2] It is the only remaining covered bridge in Philadelphia and is the only covered bridge in a major US city.
Name Image County Location Built Length Crosses Ownership Truss Notes Ashland Covered Bridge [1]: New Castle: Ashland: ca. 1860: 52 feet (16 m) Red Clay Creek
Covered bridges are timber-truss bridges with a roof and siding which, in most covered bridges, create an almost complete enclosure. [1]The purpose of the covering is to keep snow from accumulating—winter snow accumulation could easily collapse a bridge, and the steep roof would tend to shed snow to either side.
The World Guide to Covered Bridges is published by the National Society for the Preservation of Covered Bridges (NSPCB). [1] It uses a covered bridge numbering system developed by John Diehl, the chairman of the Ohio Covered Bridge Committee. The committee first used the numbering system in 1953 to publish a list of covered bridges in Ohio. [2]