History of Steel Joist

How web truss is a unique and efficient structure. The complicated structure in the areoplane's wing can be showed in the section of it. Therefore, the main force is beared by top and bottom chords and webs that is truss which is an old and current topic. Truss structure was also used in Waibaidu Bridge of senic spot in Shanghai. Shanghai World Finance Ceter was designed at height of 460m. The main body of the building shows us a huge verticle truss which prove the reasonable solution of truss structrue.

Truss structure is the final solution for horizontal member which is set up by smallest quantity material and have best bearing capacity.

The first joist in 1923 was a Warren truss type, with top and bottom chords of round bars and a web formed from a single continuous bent bar. Various other types were developed, but problems also followed because each manufactrure had his own design and fabrication standards. Architects, engineers and builders found it difficult to compare rated capacities and to use fully the economies of steel joist construction.

Members of the industry began to organize the Institute, and in 1928 the first standard specifications were adopted, followed in 1929 by the first load table. The joists covered by these early standards were later indentified as open web steel joists, SJ-Series.

1953- Introdction of Longspan Steel Joists, L-Series. Specifications and a standard load table covering spans through 96 feet and depths through 48 inches, were jointly approved with the American Institute of Steel Construction.

1959- Introduction of the S-Series Joists, which replaced the SJ-Series Joists. The allowable tensile stress was increased from 18,000 to 20,000 psi, joist depths were expanded through 24 inches, and spans increased through 48 feet.

1961-a Introduction of the J-Series Joists, which replaced the S-Series Joists. The allowable tensile stress was increased from 20,000 psi to 22,000 psi, based on the use of steel with a minimum yield strength of 36,000 psi.
b. Introduction of the LA-Series Joists, which replaced the L-Series Joists. The LA-Series Joists allowed a tensile stress of either 20,0000 psi or 22,000 psi, depanding on the yield strength of the steel.
c. Introduction of the H-Series Joists, whose design was based on steel with a minimum yield strength of 50,000 psi, and an allowable tensile stress of 30,000 psi.

1962- Introduction of the LH-Series Joists, utilizing steel whose minimum yield strength was between 36,000 psi and 50,000 psi.

1965- Development of a single specification for both the J-and H-Series Joists by the Steel Joist Institute and the American Institute of Steel Construction.

1966- Development and introduction by the SJI and AISC of the LJ-Series Joists, which replaced the LA-Series Joists. Also, the development of a single specification for both the LJ-and the LH-Series joists, with the use of 36,000 psi minimum yield strength steel for the LJ-Series, and 36,000 psi to 50,000 psi minimum yield strength steel for the LH-Series.

1970- Introduction of the DLJ-and DLH-Series Joists to include depths through 72 inches and spans through 144 feet.

1971- Elimination of the number 2 chord sizes and the addition of joist designations 8J3 and 8H3 to the load tables.

1972 a Adoption by the SJI and AISC of a single specification for the LJ-, LH-, DLJ-, and DLH-Series Joist.
B Adoption by the SJI and AISC of the expanded specifications and load tables for the Open Web Steel Joists which increased the depths through 30 inches, and the spans through 60 feet, plus adding chord sections 9,10, & 11.

1978-a Elimination of the J-,LJ-, and DLJ-Series Joists because of the widespread acceptance of high strength steel joists.
B Introduction of Joist Girders, complete with specifications and weight tables, in response to the growing need fro longer span primary structural members with highly efficient use of steel.

1986- Introduction of the K-Series Joists, which replaced the H-Series Joists. The reasons for developing the K-Series Joists were (1) to achieve greater economies by utilizing the Load Span design concept, (2) To meet the demand for roofs with lighter loads at depths from 18 inches to 30 inches; (3) To offer joists whose load carrying capacities at frequently used spans are those most commonly required; (4) To eliminate the very heavy joists in medium depths for which there was little, if any, demand.

Joist Enterprises' Organization in USA

American SJI-Steel Joist Institution, which founded in America in 1928, is a non official and profit organization serving as the research institution of trade technology and functional department of distributing industry code. American SJI has altogether 35 member enterprises locating at various states of America and Canada with annual capacity of steel joist of over 800 thousands tons.

In America, each steel joist enterprise develops his truss detail separately and differently. But the data of joist span, member size and load value must be selected from Standard Load and Weight Table provided by America SJI. Any new steel joist section developed by specific enterprise has to be rechecked and approved in written by SJI before distributing the finished products on the market.

Using of Steel Joist in America:
In fact, steel truss was not invented by American. It will be clear to visit Waibaidu Bridge at North Bund Shanghai built by British men in 1907. But the credit goes to the American because they really developed steel truss as structural products which can be broadly used and fabricated in massive production.

History of Steel Joist Development in China

History of Steel Joist Development in China:
Steel truss structural system was used in bridge building at the emergence of it. Therefore, China earliest steel truss structures were all various steel structure bridges. Around 1950s, along with the adoption of hot rolled profile steel in construction, steel welding truss was used in certain degree in China industry construction field. Nowadays, we can learn about it from Roof Truss Standard Detail and Steel Truss Crane Beam Standard Detail. But due to lower steel turnover and easy to rust by poor quality, steel truss structure was not broadly used and normally considered as concept of shed and temporary house during that time.

Until 90s of last century, along with pre-engineered building foreign company entering into China, steel truss secondary products have been imported with their advanced design technology. At that time, steel joist is completely imported from abroad.
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In 1994, Shanghai Kangqiao Hengtong Exhibition Hall Project, floor steel joist of 40 thousand square meters, joist imported by Meidong Corporation from America.
In 1995, Shanghai Rinnai Water Heater Project with adoption of floor steel joist imported from America.
In 1996, Hitachi Shangling Washing Machine Project located at lot of 4B of Shanghai Jinqiao area, 23 thousands square meters of floor steel joist completely imported from America.
From 1997 to 2004, portal frame steel structure is developed greatly in China. Due to high transportation cost, the projects with imported steel joist reduced.
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At the end of 2004, Shanghai Open Steel Joist Corporation was founded. During the post three years, steel joist was used in near hundreds of projects.
In 2008, second Open fabrication base was in construction. A new start poit was set for China pre-engineered steel joist industry.