SBCA Recommends Solution to AWC Regarding Shear Wall Design Values

Originally published by: SBCAJuly 9, 2014

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It's easy to identify problems or issues in your company or in the marketplace. The greater challenge is formulating preferred solutions. Some problems have easy solutions, but others have complications that are not easy to solve. Further, innovation, status quo traditions, market threats, market opportunities, and bureaucracies can all have a significant influence on transparently finding a desired solution. For trade associations like SBCA, successfully navigating these kinds of market obstacles, even when a clear solution is evident, can prove difficult.

SBCA believes engineered solutions should have great value in the market, and sound fundamental knowledge is important to creating change that adds value to engineered and structural building component solutions. We as an industry believe change through innovation is for the best, because innovation helps mitigate threats to our industry and allows our value opportunities to grow.

As a pertinent example, the following has been stated by AWC staff in response to SBCA’s point of view on shear wall design values:

“Issues in the SBCA letter were raised at the July 2012 WDSC meeting.  Kirk Grundahl presented information similar to the information provided in Figure 5 of Lawless 1.pdf.  In general, the discussion highlighted the problems with using non-standard test procedures resulting in undefined levels of overturning restraint which is not the basis of reference nominal unit shear values in SDPWS. There were no specific changes proposed at that meeting. At TG meetings, participants were invited to provide specific changes for the TG to consider - all specific proposals for change were considered”

SBCA has consistently used standardized testing per SBCRI’s accreditation, and has made clear recommendations for what test data suggests are more reasonable nominal unit shear capacity (NUSC) values, given actual real-building-performance characteristics of wood structural panel (WSP) shear walls. SBCA recommends these test values should replace the NUSC values given in SDPWS Table 4.3A as shown below, or that SPDWS provide deeper understanding on how the NUSC values were derived. From there, it is important to reconcile the real-building-performance test values to each cell of Table 4.3A. This information will allow all engineers to fully understand the test data, design value development methods and the judgments made to arrive at the Table 4.3A values. This knowledge is important in order to make good engineering judgments for actual downstream applications.

Clearly, SDPWS NUSC values are the same as the International Building Code (IBC) NUSC values, so this process applies there as well.

These recommendations were provided in SBCA’s September 9, 2013 letter to APA-The Engineered Wood Association, and in SBCA's June 10, 2014 letter to AWC as follows:

"Based on the knowledge that we have, we believe we have done our due diligence and provided a recommended revision to table 4.3A as follows:

Based on the minimum tested ultimate capacities, a very reasonable, extremely representative, and conservative NUSC value is 475 plf (this is 515 plf in SDPWS which yields a 10% advantage over test data) and 535 plf (this is 672 plf in SDPWS which yields roughly a 25% advantage over test data) for WSP shear walls fastened with 6d (0.113" dia.) and 8d (0.131" dia.) nails respectively, including 24” o.c. stud spacing. Table 1 below is an example of a possible revised version of SDPWS Table 4.3A."

This is the starting point of our recommendation. As stated above, there may be recommendations that also account for reconciliation between the SBCRI test data and current SDPWS NUSC values. It seems as though this reconciliation would be best performed based on an in-depth knowledge of the origins of the SDPWS NUSC values.

SBCA has also consistently made the following recommendation for reasonable design values to replace those in the International Residential Code (IRC):

IRC-based braced wall panel applications that meet the requirements of Section R602.10 should have the following values, based on SBCRI testing. As you can see, when the IRC provides a solution that cannot be supported by testing of real buildings in a code-compliant application of braced walls, more accurate and technically correct engineered solutions will never be able to compete. For more information about this table and the facts behind it, please contact Larry Wainright.

R602.10.4.4 Design Values. For the purpose of braced wall design, the capacity of wood structural panels to resist lateral loads, as found in Table R 602.10.3(1) are found in Table R602.10.4.4.

The SBCA proposed transparent publishing of IRC NUSC values were, previous to SBCRI test data showing the same, confirmed through APA testing entitled, “A Review of Large Scale Wood Structural Panel Bracing Tests,” which was a report to the BSSC Bracing Committee in May 2007.

It remains reasonable to assume raw material suppliers to the SBC industry are responsible to ensure their products have well known, well understood and transparently accurate design properties. Further, all building designers, buyers and end users should be in a position to easily access all design considerations and any relevant factors (i.e. system effect factors, etc.) that should be considered during the design process. This includes providing all the considerations that are needed for successful application or installation.

It is clearly okay to have the design process include a system effect factor. It would be even better for every user of WSPs to know exactly what this factor is, exactly where it came from and the boundary conditions surrounding its use.

As of yet, no one has brought similar testing to the table to show where the above recommended SDPWS, IBC and IRC NUSC value assessments are incorrect. As such, SBCA has every reason to believe its conclusions are correct.

This can easily be seen as disruptive to the status quo and extremely difficult to change in the current building code development environment. The difficulty involved with the code change process is a good thing for those that have a codified competitive advantage. There is a disincentive to change when one’s advantage is written into the law.

Left hidden, this leads to a law-based competitive advantage forever. When known and unresolved, by those that can take action to resolve this, the competitive advantage remains, but then comes with an assortment of downstream implications.

SBCA persists in its belief that all industries are best served by having a transparent understanding of real WSP NUSC values. Until the needed changes take place everyone must rely upon the derivation of design values, which have been codified into law through the codes and standards (e.g., IRC, WFCM, IBC, SDPWS, etc.) and use those as performance benchmarks.

APA, AWC and the ICC seem to be the responsible parties with respect to  code language justification and efficacy. The foregoing information must, by law, be allowed to be used in the context of the law that says, “that the material…..offered is, for the purpose intended, at least the equivalent of that prescribed in this code.” 

There is the potential for many innovative products to be equivalent in performance to WSP panels, if the real performance and design methodology characteristics of WSPs were transparently defined. While certainly concerning for WSP suppliers, like football and many things in life, competition makes all businesses better.

Innovation and change is also the stated intent of IBC Section 104.11 and IRCSection R104.11 (IFC Section 104.9 is similar) where it says:

104.11 Alternative materials, design and methods of construction and equipment. The provisions of this code are not intended to prevent the installation of any material or to prohibit any design or method of construction not specifically prescribed by this code, provided that any such alternative has been approved. An alternative material, design or method of construction shall be approved where the building official finds that the proposed design is satisfactory and complies with the intent of the provisions of this code, and that the material, method or work offered is, for the purpose intended, at least the equivalent of that prescribed in this code. … Where the alternative material, design or method of construction is not approved, the building official shall respond in writing, stating the reasons the alternative was not approved.[1]

The foregoing describes what SBCA believes is true and what has become the law. Those that are responsible for the law can change the law when new information is provided, if deemed relevant to do so.

Free and unfettered competition as the rule of engineering and trade seeks there to be no double standards. In this case, without transparent knowledge, the “at least the equivalent” has been, and can continue to be used to severely limit competitive access to a market. This does not serve building designers, the overall building community or the general public well.

[1] The last sentence is adopted language in the 2015 codes.


PDF icon sbcas_sept_9_2013_letter_to_apa.pdf2.17 MB

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