Accuracy in FTAO Wood Shear Wall Design Methods

Are you using the most accurate design method when you utilize Force Transfer Around Openings (FTAO) in your wood shear wall design? In the past, a variety of design techniques have been used to determine a rational analysis for wood shear walls, but recent research sheds some light on which methods are the most accurate for this type of design.

In the July 2016 SE University Core Session, Karyn Beebe, PE, LEED-AP, from APA – The Engineered Wood Association, covered Advancements in Force Transfer Around Openings for Wood Framed Shear Walls. During her presentation, Karyn highlighted recent results from research completed in a partnership between APA, University of British Columbia, and USDA Forest Products Laboratory. This research examined the internal forces generated during full-scale testing of a variety of walls with code-allowable openings of various sizes, and compared those forces with various design techniques and computer analytics that mimic testing data. The results proved to be very useful to determine which design methods would be most accurate for design engineers to implement in their FTAO wall designs.

As shown in the following table, a summary was created for 8 different wall configurations for FTAO, and compared the measured internal forces with the predicted forces from 4 different design techniques: The Drag Strut and Cantilever Beam Techniques, both developed by Zeno Martin, the Diekmann Technique, and the SEAOC/Thompson Technique. The first column shows the measured strap forces around the openings and the remainder of columns give the percent error in the predicted strap forces for the 4 methods. As you can see, the blocks highlighted yellow show an unconservative design (less than 100%), while the green blocks show an overly conservative design (greater than 300%). In most cases, the Diekmann and SEAOC/Thompson Techniques were useful in determining accurate strap forces. One outlier would be for Wall 6, which was a C-shaped panel, where the Drag Strut Technique was the best predicted response of strap forces.

Measured vs Predicted Strap Forces

Click on the picture for an enlarged view

As a design engineer, this information can be used to identify which design techniques would result in the most efficient design for our clients, depending on which type of shear wall is being used on any given project. To learn more about this recent research, Karyn provided a link to a full set of testing results that can be viewed on the APA website’s Resource Library. Registration is required to access the file, but there is no charge to register and access other documents in the Resource Library.

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