Good Information Leads to Good Decision-Making
Good Information Leads to Good Decision-Making
can transform your market.
Over the past year, you may have noticed a significant increase in the frequency of articles in SBC that provide an overview of structural test data and engineering concepts. There are several reasons behind this effort, the most important of which is to publicly share our knowledge and understanding of real-world structural performance of various aspects of the building envelope.
Why is this so important? First, because the structural building components (SBC) industry is, at its core, about providing engineered framing solutions. Second, effective engineered framing solutions rely on accurate design values for the raw materials and fasteners that are utilized. Third, initial empirical data collected through the SBC Research Institute (SBCRI) indicates the prescriptive building code can undervalue engineering by overstating the performance of certain conventional framing methods and materials.
The code accomplishes this by incorporating into the design values an unknown amount of systems effects, or by reducing the building’s overall factor of safety. Neither of these adjustments are quantified or well defined in prescriptive code provisions. This results in prescriptive materials having design values higher than what real empirical test data suggests they are. This can make it very difficult for engineered framing solutions to compete, because the prescriptive solutions supported through the code appear to be more efficient.
Conversely, the goal of generating SBCRI empirical data is to fully understand real performance and place this information in the hands of the SBC industry’s engineering community. Ultimately, this knowledge will enable significant innovation to occur, with the goal of growing SBC industry market share.
This article will briefly explore each of these concepts and then outline how SBCA and SBC Magazine plan to serve the SBC industry by broadly communicating what we have learned, and what we anticipate to learn in the future, through SBCRI testing.
SBC Industry Is Engineering Based
One of the greatest strengths of the SBC industry is its ability to provide builders an engineered solution to any load path and framing challenge. Whether the builder wants to achieve large, open room layouts, multi-planed roofs or significant improvements in the energy efficiency of the building envelope, component manufacturers (CM) most often can design and produce what their customers want and need.
The SBC industry’s engineering community creates considerable value to its customers by providing these types of value-added products. Within that community, each company’s team of designers can differentiate themselves through creativity, engineering acumen and superior production techniques. Just like snowflakes, no two component solutions need be alike, and that ultimate flexibility is the reason why components are a superior framing method.
The proprietary design software used by CMs is an incredibly powerful tool. In the hands of the SBC industry’s engineering community, this software allows for even more creative, efficient design work than what was possible in the past. Further, it allows CMs to tackle building material challenges in all three dimensions by providing the building’s coordinate geometry (i.e., enabling a building information management, or BIM, approach).
This gives CMs the ability to collaboratively solve design issues with a builder, architect and/or engineer of record much more quickly than the days or weeks it took in even the recent past.
Engineering Relies on Accurate Design Values
At the heart of the SBC industry’s design software are fundamental engineering equations and assumptions based on generally accepted engineering practice. Within those equations, industry-published raw material design values are input based on the assumption that the design values formulated by their providers are accurate and consistent. For a thorough understanding of this topic, read the article “Design Values Matter: Make Sure You Fully Understand Why” (April 2013).
As the Southern Pine design value change process illustrated, the SBC industry’s ability to gather its own empirical data on these raw material design values through SBCRI is invaluable. This issue was also discussed in great depth by a couple of CMs in the article “Knowledge Is Power: Quantifying the Value of SBCRI through SP Design Value Changes” (Sept/Oct 2014).
What both of these articles explain in different ways is that everyone in the building industry purchasing raw materials, such as lumber, for conventional framing or structural component applications is actually buying design values and related properties that are then incorporated into National Design Specification (NDS) engineering equations. These equations are used by engineers, and their design software programs, to accurately estimate the raw material’s ability to resist applied loads, and consequently a reliable and safe load path. If the producers and suppliers of those raw materials aren’t willing to stand behind the design values they ascribe to their product, it becomes exceedingly difficult for anyone to accurately engineer a structure.
The International Residential Code (IRC) is a good example of the dilemma faced by the SBC industry. Often, engineers default to using the IRC over an engineered solution because, as pointed out earlier in this article, the IRC through the means by which it is put together, provides a more economically efficient solution. This may sound amazing, but it’s true. Further, the unsupported assumptions that make up some of the IRC solutions have been brought repeatedly and publicly to the attention of the International Code Council (ICC), which develops the IRC and other model building codes. It remains unclear what action, if any, the ICC will take to begin correcting this obvious flaw.
One of the primary goals of SBCRI is to help the SBC industry fully understand fundamental raw material design values and their single-element engineering performance. With this knowledge, it is possible to gain an even better understanding of the performance of those raw materials when testing them in a real-world assembly. At the end of the day, reliable and safe building performance is completely dependent upon accurate design properties, engineering precision and a complete understanding of all the design assumptions and engineering considerations needed for successful application or installation. Said another way, unreliable or inconsistent lumber and wood structural panel (WSP) design values lead to unreliable or inconsistent load path resistance or an unknown factor of safety.
Building Code Undervalues Engineering
One of the most important reasons to broadly communicate the empirical data collected through industry-related testing at SBCRI is to more accurately define what it means to provide reliable engineering in the context of meeting the mission of the building code (i.e., to establish minimum requirements to safeguard the public safety). Unfortunately, the building code development process has become a more relational and political exercise, versus relying on hard science and engineering. This fact further undermines the value of good engineering. Raw material design values and building material performance characteristics can easily be written into the building code, whether they are scientifically correct or not, and become law when states and local jurisdictions adopt them.
Over the past several months, SBC Magazine has begun the process of exploring some of the ways in which this presents a significant challenge to the SBC industry. For example, the articles “You Don’t Know What You Don’t Know, Part II” (Sep/Oct 2013) and “Installation of Interior Gypsum Board Finish” (November 2014), examine the way that the prescriptive provisions of the building codes provides a significant competitive advantage to WSP braced wall panels. While APA testing performed for their Building Seismic Safety Committee (BSSC) indicates the real lateral resistance of an isolated WSP braced wall panel without interior ½" regular gypsum wallboard applied has a lateral resistance design value of 351 plf, the IRC provides a value of 600 plf. Similarly, the same wall panel with interior ½" regular gypsum wallboard has a lateral resistance design value of 383 plf, but the IRC assigns it a value of 840 plf.
A similar situation exists in the code with respect to the development of WSP seismic design coefficients in ASCE 7 Chapter 12 Table 12.2-2. The articles “Seismic Design Coefficients, Part I” (May 2014) and “Seismic Design Coefficients, Part II” (August 2014) explore the unfair advantage WSP performance is granted through the code. As a consequence, newly developed alternative products may fail to meet the subjective equivalency parameters created and placed into ASCE 7, and thus be considered not equivalent even when they have equivalent or better performance than WSP shear walls.
This situation is compounded by the fact there is no rational seismic design parameter (SDP) development solution in the building code. As a consequence, SBCA developed a closed-form, mechanics of materials approach to SDP creation. This new approach is simple and rational, particularly when compared to some of the other approaches currently used in the market (see the sidebar on page 25, which includes statements from an AC130 task group that appear to indicate it is acceptable to make up engineering mechanics to fit a given WSP marketplace outcome). This is significant for CMs in high seismic areas who are attempting to design innovative components.
AC130 is a proprietary Acceptance Criteria (AC) entitled “Acceptance Criteria for Prefabricated Wood Shear Panels”* and are established by an ICC-ES committee to provide a basis for issuing ICC-ES evaluation reports on products and systems under the codes referenced. Acceptance criteria are copyrighted publications of ICC-ES and are developed for use solely for purposes of issuing ICC-ES evaluation reports to applicants. Acceptance criteria are available to the public for purchase, but they are not for use outside of the ICC-ES system
Statements from the AC130 task group illustrate this as follows:
- Since the limits on the three parameters are not based on the minimum tested parameter, some of the WSP tests in the database will fail to be equivalent.
- This was determined to be acceptable by the Task Group as seen by the following quote:
“The Task Group consensus was that whenever possible, the upper and lower bounds for a parameter would be established to encompass a reasonable range of the benchmark data. This was accomplished using the concept of average plus or minus one standard deviation. This technique provides data-driven limits tied directly to the expected range of the code-defined system, yet also supplies some leeway based on known variability in the target benchmark system. The alternatives, either targeting the absolute extremes from the database or using some form of mean basis were rejected. The former was judged to be too ‘loose’ a criteria and the latter was judged to be too restrictive given that half the benchmark database would fail to qualify any given criterion.”
- Of the 48 tests in the AC130 database, 14 (or 29%) are not equivalent.
- This means that a product that is truly equivalent to one of the walls in the AC130 database may be rendered to be NOT equivalent inappropriately by AC130.
- This was recognized by the Task Group as seen in the following statement:
“Given the large variation in performance expected with all possible building code-permitted permutations of the benchmark (i.e., wood structural panel) system, the Task Group judged that it was not appropriate for the proponent of a prefabricated shear panel to simply select test data from a single (WSP) shear wall configuration to prove equivalency. Performance criteria established using this single data point may or may not be representative of the level of performance commonly associated with the population of walls (i.e., the 48 walls of which 14 failed the task group criteria) that conform to the code-defined benchmark system.”
In other words, the level of performance and acceptance criteria of the WSP walls was set in such a way that WSP walls that failed to meet the acceptance criteria were deemed to comply, and a different set of rules apply to alternative competing products.
- The Task Group further states that: “It was acknowledged that the cyclic shear wall test data sets available to serve as a benchmark for any code-defined lateral force resisting systems would be limited and not provide a comprehensive and statistically valid representation of all possible permutations of the code-defined system.”
- Therefore, the rules were set to favor one class of products over all other competing products. Further, it was fully recognized that it is possible to test WSP shear wall configurations that do not meet the AC130 equivalency parameter limits but will still use the same seismic design coefficients regardless of their failure to meet the AC130 equivalency criteria.
Empirical Data Allows Innovative Engineering
How does the SBC industry know these competitive advantages exist within the prescriptive provisions of the building code? It didn’t, at least it didn’t have proof, until these issues were revealed through structural testing conducted at SBCRI. The good news is that, through the data SBCRI is able to collect, the SBC industry is not only able to expose the inequalities, it can actively do something about it. Professional engineers can provide significant value because they have the ability to assess the empirical test data, do comparative analysis and make value judgments based on their expertise. In other words, they have the ability to innovate.
In his article, “Innovative Framing: A Concept for Today & Tomorrow” (August 2014), SBCA Past President Scott Ward made the following observations that bring this concept to its logical conclusion: “… the building code clearly gives us the flexibility to find a better way to frame a building. We do this as a matter of course by reducing material usage to save cost and/or make production and installation easier. The process we use to design and manufacture a structural component lends itself well to finding an innovative framing solution that meets or exceeds our customers’ expectations. In fact, we have to do this on every job; otherwise, our customers look elsewhere.
“Further, our industry is set up to facilitate innovative framing by bringing together material suppliers, building designers, builders and framers. We are driving innovation through communication and collaboration, allowing everyone in the chain to reap the benefits of the tools and capabilities we have to design a building where the complete load path required by the code can be constructed in the most efficient and cost-effective way.”
Ultimately, the more detailed understanding of actual building performance possible through SBCRI testing data should lead the SBC industry to more accurate and cost-effective roof truss, wall and floor truss/I-joist designs because the correct loads get placed in the proper location, and design is based on actual loading conditions, not tradition-based assumptions.
The Power of Communication
Testing at SBCRI has just begun to prove that what everyone thinks they can count on, and are getting from a variety of standardized test methods or building code requirements, may be wrong. The SBC industry’s engineering community is regularly competing against prescriptive code perceptions as opposed to real-world building performance. The real question is how individual CMs can overcome this challenge.
As stated earlier, the best and most effective approach is with science. In 2013, SBCA and the Truss Plate Institute (TPI) entered into an industry testing cooperative agreement to jointly fund testing at SBCRI to address fundamental engineering issues facing the industry. An Industry Testing Subcommittee made up of CMs was formed to compile and prioritize a list of structural issues to create test plans. Those test plans are then reviewed by members of SBCA’s Engineering and Technical Committee and TPI’s Technical Advisory Committee (TPI TAC), who review and provide feedback both on the initial test plans and analysis of the resulting data.
Once the SBCRI testing is complete, the data is shared with SBCA members through the SBC Magazine website. SBCA members will be alerted to this information through member-only SBC Industry News–Special Edition emails. The membership invested in SBCRI and, as a consequence, is the first to benefit from the knowledge gained through testing.
Exposure to this information can lead to several outcomes. One of the most promising is the idea that individual SBCA members may take this information and find ways to use the data to innovate on their own through generally accepted engineering practices. The data will also be provided to TPI TAC, which then is charged with using the data and engineering analysis to provide SBC industry-wide solutions.
Online Source for Test Data & Analysis
The end goal of this work is for test data, data analysis, engineering mechanics concepts and generally accepted engineering considerations to eventually be published on the SBC Magazine website, where it can easily be reviewed, revised and updated, and always be available for public review. Much like the past articles referenced here, SBC will continue to publish and provide the entire market with the knowledge gained through testing. This public forum will give the broader engineering community the opportunity to evaluate and comment on the analysis, either confirming the conclusions reached or providing additional opportunities to refine the data and analysis.
Our assumption is there is sufficient interest in the engineering and code development community at large to get the science right. If we publish something that is incorrect, we will get the feedback needed to correct it (or, at least, point out where we need to do further testing and/or analysis).
Once the public vetting process has run its course, the data and analysis will be published in SBCA Research Reports and made available to the market in a well-organized online database on SBCA’s website. SBCA Research Reports can then be referenced in a wide variety of ways to serve the best interests of SBCA members and to advance sound science, engineering, code development and market education.
* ICC-ES website links of interest: 1) http://www.icc-es.org/Criteria/criteria/dsp.cfm?ac_code=AC205, 2) http://www.icc-es.org/Applications/rules_ec_Dec2012.pdf, 3) http://www.icc-es.org/News/cold-form-steel.shtml and 4) http://www.icc-es.org/Criteria_Development/1212-alt/AC130.pdf