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The Queenpost Truss Covered Bridge

Queenpost Truss Bridge Truss Diagram

The next range in span lengths commonly includes trusses developed from a simple modification of the kingpost. The queenpost truss is, conceptually, simply a stretched-out version of the kingpost truss, accomplished by adding a central panel with extra horizontal top and bottom chords. Classic examples of queenpost trusses do not have any diagonal web members in the central rectangular panel. Therefore, the most simple queenpost trusses are not true trusses at all,; but rather frames. The vertical members are termed queenposts. These trusses are considered to have three panels.

The member forces and behavior in queenpost trusses are very similar to those found in kingpost trusses: therefore, the design considerations for these two basic truss styles are equally similar. A number of similarities exist between kingpost and queenpost trusses:

Truss components are usually of single members.
The key area of interest is the heel connection.
Some of the longer spans use subdivided panels, with subdiagonals, hanger rods, and extra floor beams.

The span lengths of queenpost truss bridges range from about 12.2 to 18.3 m (40 to 60 ft), although there are a few examples that are longer. The longer span requires that many of their bottom chords be spliced longitudinally from separate timbers. This tensile connection is another area of weakness in the truss.

There are approximately 101 bridges supported by queenpost trusses, or slightly more than 10 percent of all the surviving covered bridges in the United States. Their spans range from 7.6 to 39.6 m (25 to 130 ft), and they were built between 1845 and 1985.