Graphical Construction Glossary >> Roofs and roofing. >> Roof Trusses >> bowstring truss

Bowstring Truss

A roof truss that has the top chord in the form of a circular or sometimes a parabolic arc. Know to be economical over large spans.

Also known as a Belfast Truss

A prefabricated Belfast roof truss.

In the photo above we are looking at quite flat bowstrings that have a curved top chord. These trusses are spanning about 18M. They are made up on site from prefabricated kits using lightweight MS angles flat and plate connectors. Bolted together to form the trusses.

Top chords can also be segmented straight sections as seen in the lower sketch. Bottom chords are usually slightly cambered.

The author has experience working with a timber engineering company that made trusses up to 100ft. span using laminated softwood. The bottom chords had a camber of around 1" every 10ft. At that time, (in the early 1960's) prior to the advent of cheap steel systems, these timber bowstrings were the most economical way of clear span roofing sheds and warehouses.

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