Open-Web Steel Joists
by D. Matthew Stuart
Focusing on structural engineering issues involved in the repair, restoration, or adaptive reuse of older buildings for which drawings no longer exist, this article is the eighth in a series about antiquated structural systems that can be adapted or reanalyzed for safe reuse. — Editor
Most of the systems that have been discussed in this series are no longer in use because they have been replaced by more innovative or more economical methods of construction.
This article deals with a method of construction that is still very much in use today: open-web steel joists. Nevertheless, the historic, original construction practices may still be encountered in existing structures.
I would like to thank the Steel Joist Institute (SJI) for providing much of the material that was used in the development of this article.
According to a brief history of open-web joists published by the SJI, the first Warren-type, open-web truss/ joist was manufactured in 1923, using continuous round bars for the top and bottom chords, with a continuous bent round bar used for the web members.
Five years later, in 1928, the SJI was formed, and it adopted the first standard specifications for open-web joists. This initial type of open-web steel joist later became identified as the SJ-Series. In 1929, the first SJI load table was published.
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This article is adapted from the June 2009 and November 2009 issues of STRUCTURE magazine, with permission of the publisher, the National Council of Structural Engineers Associations (NCSEA).
The Eames House in Pacific Palisades, California, designed by Charles Eames, was built with a selection of manufactured steel structural elements, including open-web steel joists, which provide the primary roof structure.
Photo: Tim Street-Porter, Elizabeth Whiting & Associates, London
The lightweight open-web steel joists of the Eames House (designed and built 1945 to 1949) feature webbing made from a continuous bent steel rod.
Photo: Flickr user "lotsinspace"
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