| attessswelino | Дата: Воскресенье, 21.07.2013, 22:57 | Сообщение # 1 |
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| The structure in photo 1 was built around 1960, and used the bowstring truss so that there would be a large unobstructed floor area for retail sales and so that the roof would easily shed rain and melting snow. These trusses are usually built of either wood or steel, although some have wood for the top and bottom chords and steel for the web members. Bowstring trusses were originally designed for bridges, but became popular during World War II to support the long roof spans of aircraft hangers and manufacturing facilities.
Throughout past decades, fires in buildings with bowstring truss roofs have caused catastrophic structural failures that have claimed the lives of firefighters. http://superkran.netau.net Among these were the 1988 Ford dealership in Hackensack, New Jersey, and the 2012 theater fire in Abbotsford, Wisconsin. Search the Internet for "bowstring truss"; http://superbuild.hostoi.com "bowstring truss fires"; "Hackensack Ford fire"; "Abbotsford Theater fire"; and similar. Also visit the NIOSH firefighter fatality Web http://building.comlu.com to review reports of these and other firefighter fatalities.
Trusses have been in common use in North America since before 1800. Some truss designs were developed for bridges and adapted for use in buildings. Photo 2 shows a timber roof truss in a "mill" (the ancestor of modern Type IV or heavy timber) building from 1840. The compression members of this truss are of wood, ranging from 8 x 8 inches to 12 x 12 inches (20.3 x 20.3 cm to 30.5 x 30.5 cm). The tension members of this truss http://besttech.comlu.com are wrought-iron rods. Search the Internet for "trusses" for information on their history and design.
Photo 3 shows the trusses supporting the ceiling and roof assembly of a church, built in the late 1800s. The ceiling in this church is attached to the bottom of the same rafters that support the roof. These trusses are not only decorativea?”they support the ceiling and roof.
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