A little bit of Joist history…

How about a little bit of joist history?

Currently on the market, there are essentially three different types of engineered floor joists

  • Wood I-Joists
  • Steel plated floor trusses
  • Finger-jointed and glued floor joists

Wooden I-Joists

They’ve been around for nearly 50 years, having been invented in the late 60’s. They get their name from their cross-section, which is shaped like an “I” with flanges at top and bottom and a thin web section between). Originally, flanges were made of solid sawn lumber and the web was plywood.  Flange material changed over the years to include LVL and PSL and those are still used today, along with solid sawn lumber.  Web material has switched 100% to OSB.

Steel plated floor trusses

The first real engineered wood joist was invented in the early 50’s in Florida when Carroll Sanford developed the steel truss plate and used it to produce steel-plate-connected parallel chord floor trusses, with open web. Each plated floor truss is custom-designed and fabricated to exact job dimensions. Steel-plate-connected floor trusses are produced in local fabrication plants and are not identified by national brands.

There are a few open web joist products that use steel plate connectors and operate under national brands, though.  These products feature trimmable ends so they may be produced in volume and shipped to jobs without requiring the type of engineered design necessary for normal plated trusses.

Finger-jointed and glued floor joists (Open Joist)

A new product type has more recently become available in the United States: an all-wood, open web, trim-able floor joist.  This product, known as OPEN JOIST, was invented in Canada in the 1980’s and was the original trim-able floor joist. It started out as what was called the Open-Joist 2000, available in one-foot increments with 11” of trimmability. It developed into what is now called the Open-Joist Triforce® which as 24’’ of trimmability.

Open Joist uses a combination of I-Joist and truss engineering and its published values are come from actual testing, not from calculations.

Instead of steel plates, this products flanges and webs are connected with precision finger joinery and structural adhesive.  This technology results in efficient use of wood fiber and reduced weight since web dimensions are not required to match flange dimensions.

Because they are “stock” joist with constant values, standard repair details for common jobsite mishaps and improper alterations have been engineered in advance and are available to job superintendents.

Hope you enjoyed this very brief joist history. If you’d like to know more about Open-Joist Triforce® please don’t hesitate to contact us.

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