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The Burr Arch Truss—or, simply, Burr Truss or Burr Arch—is a combination of an
File:Burr Truss P4230099 Sims Smith.jpg, Sim Smith Covered Bridge, Parke County, Indiana. Notice the arch projects below the lower chords of the bridge.
File:Burr Truss (2 span) P4230017 Mansfield CB (Parke Cty).jpg, Mansfield Covered Bridge, Parke County, Indiana. The roof was missing after a major storm and the interior design was easier to see.
File:Burr Truss (2 span) P4230125 Mansfield CB (Parke Cty).jpg, Mansfield Covered Bridge. Spans could be added to extend the bridge further than bridges of similar design.
File:Burr Truss (3 span) 011 09A (Medora, Jackson Cty).jpg, Medora Covered Bridge, Jackson County, Indiana. This is the longest covered bridge in Indiana.
arch
An arch is a vertical curved structure that spans an elevated space and may or may not support the weight above it, or in case of a horizontal arch like an arch dam, the hydrostatic pressure against it.
Arches may be synonymous with vau ...
and a ''multiple kingpost'' truss design. It was invented in 1804 by Theodore Burr, patented on April 3, 1817, and used in bridge
A bridge is a structure built to span a physical obstacle (such as a body of water, valley, road, or rail) without blocking the way underneath. It is constructed for the purpose of providing passage over the obstacle, which is usually somethi ...
s, usually covered bridge
A covered bridge is a timber-truss bridge with a roof, decking, and siding, which in most covered bridges create an almost complete enclosure. The purpose of the covering is to protect the wooden structural members from the weather. Uncovered woo ...
s.
Design
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. The opposite view is also held, based on computer models, that the truss performs the majority of the load bearing and the arch provides the stability. Either way, the combination of the arch and the truss provides a more stable bridge capable of supporting greater weight than either the arch or truss alone.Gallery
The U.S. state ofIndiana
Indiana () is a U.S. state in the Midwestern United States. It is the 38th-largest by area and the 17th-most populous of the 50 States. Its capital and largest city is Indianapolis. Indiana was admitted to the United States as the 19th ...
has a large collection of Burr Truss bridges. Of its 92 extant bridges, 53 are Burr Trusses, many of which reside in Parke County
Parke County lies in the western part of the U.S. state of Indiana along the Wabash River. The county was formed in 1821 out of a portion of Vigo County. According to the 2010 census, the population was 17,339, an increase of 0.6% from 17,241 ...
.
Design specification
References
External links
* * {{Bridge footer Truss bridges by type American inventions Trusses