APA’s Dr. Yeh on Design Values & Responsibility
An SBCA member recently sent the following quote from Dr. BJ Yeh, P.E., APA Director of Technical Services, which provides an interesting perspective:
"Design values published by each product manufacturer are in place to provide safety and reliability to building designs," said Dr. BJ Yeh, "Therefore, the designers, building officials and consumers are expecting product performance to comply with the published design values."
While we do not have a direct reference for this quote, SBCA completely agrees with Dr. Yeh. The truss industry would make a slight modification to this statement to add clarity to the concept Dr. Yeh is advocating as follows: “Design values published by each product manufacturer (i.e. by each OSB, each lumber, each alternative product manufacturer, etc.) are in place to provide safety and reliability for designing buildings. Therefore, the designers, building officials and consumers are expecting product performance to comply with the published design values.”
Assuming that this quote from Dr. Yeh is accurate, and there is no reason to believe that it is not, SBCA members collectively believe that accurate design values are important for truss design. For example, SBCA members take responsibility for their scope of work when they provide professionally engineered and sealed truss design drawings.
Dr. Yeh is advocating that anyone using OSB or lumber in a building application can rely upon the accuracy of the design values being provided by the OSB or lumber manufacturer. When SBCA members undertake structural product designs, as Dr. Yeh states, they are buying reliable design values for OSB or lumber, based on the grade purchased. SBCA members rely upon accurate lumber and OSB design values every day as they design trusses and truss repairs. The same holds true for any product that has design values used to undertake structural design.
It follows then that all buyers of these products should consider requesting a mill specific engineer’s seal for the design values sold by that mill for the grade of OSB or lumber being purchased.
The two examples, of an engineer’s seal next to a grade stamp, are intended to make Dr. Yeh’s point. It seems like it would be easy for a lumber or OSB mill to provide a seal on design value tables for the grades and sizes that they produce.
This is really what Dr. Yeh is suggesting be done when he says, “Design values published by each product manufacturer are in place to provide safety and reliability to building designs.”
Dr. Yeh is, at the same time, implying that OSB and lumber design values are the responsibility of the OSB and lumber manufacturer. This means each OSB and lumber manufacturer should take responsibility for their product’s published grade, and associated design values via an engineer’s seal validating them.
As an alternative, since Dr. Yeh has proposed this concept, groups like APA could provide an engineer’s seal for global OSB design values for each OSB product grade. The same would hold true for lumber sizes, grades and design values by “APA like” grading agencies, including but not limited to, SPIB, WWPA, WCLIB, CLMA, Timber Products Inspection, etc.
SBCA believes that the “published design value concepts by manufacturer”, advocated by Dr. Yeh, would provide all buyers the reliability he suggests is expected. It is clear that OSB and lumber mill specific sealed design values would provide confidence in OSB and lumber engineering, so that safe and reliable building designs are the outcome.
SBCA’s hope is that all CMs begin to ask their OSB and lumber suppliers for mill specific sealed design values for each product they purchase. Dr. Yeh suggests that this is a reasonable expectation. SBCA agrees and as the saying goes, if not, why not?
Thank you Dr. Yeh for your very valuable insight.
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