Benchmark Comparison & Boundary Condition Testing Are Important
Originally published by the following source: SBCA — July 26, 2018
APA states the following, and the SBC Research Institute (SBCRI) agrees, that test results can be affected by test apparatus and real world boundary conditions (emphasis added):
5. SUGGESTIONS
- Wall bracing researchers should collect data that represents a finished large scale structure that is bracing the first of three stories. This would potentially add stiffness and dead lead along the top of the wall. This data would help calibrate where on the bracing spectrum this boundary condition is represented.
- Within each bracing type (e.g. isolated or continuous) there is a wide range of performance depending on boundary conditions. The effect of exact boundary conditions need to be quantified.
- Once the location along the bracing spectrum is established, a method for assigning design values is needed. It is suggested that the value be the lessor of the load at 0.5% drift or the peak load divided by a safety factor.
- Separate continuous and isolated bracing when examining past test data and in future code provisions. These bracing methods, while using the same wood structural panel sheathing, perform very differently.
It follows then that the only way to truly benchmark test data is to have all the test data generated by one test facility because there can be significant variation between test facilities. To get direct and reliable comparative test data to generate standard factors for OSB equivalency, a single test facility must undertake the following testing approach:
- Define what the control specimen is and all of the details.
- For example, the control braced wall panel is 15/32” OSB, 8d galvanized box nails, SPF studs at 16” o.c., nail spacing 6” on edge and 12” in field, nail edge distance at least 3/8” (this may be hard to achieve using gun nailing systems in the field), etc.
- Perform identical testing changing only one attribute of the test specimen. For example, a single change could be each of the following:
- 15/32” OSB, 1” crown staples, SPF studs at 16” o.c., nail spacing 6” on edge and 12” in field, etc.
- Another test could be 3/8” OSB, 8d galvanized box nails, SPF studs at 16” o.c., nail spacing 6” on edge and 12” in field, nail edge distance at least 3/8” (this may be hard to achieve using gun nailing systems in the field), etc.
When getting involved in a testing project, SBCRI begins with the premise that much of what has been published could have test facility effect or code provisions could have bias in some manner. Not knowing actual benchmark test comparisons can then lead to test results that appear to be non-competitive, when they actually are.
SBCRI has undertaken a wide array of benchmark comparison testing, where the only thing that changes is the sheathing material application. The following photos provide some examples:
By taking this science-based approach (the control being OSB and subsequent tests being direct and identical comparisons to OSB), SBCRI can accurately understand performance based on benchmark comparisons because everything else is equal.
When laboratories undertake testing that is only about an individual product and do not undertake benchmark comparison testing, it is easy to skew test result reporting to arrive at the answer the testing group wants to provide.
There’s a good reason why the Edward Demming said, “in God we trust, all others bring data.”
Some key questions when evaluating any reported data are: Did they use a science-based approach with respect to their testing? What is the performance of the control specimen compared to the test specimen? If the testing does not take this approach it’s important to ask why not? Is a true benchmark comparison not desired?
It may not be in the product manufacturer and/or test facility’s best interest to perform a benchmark comparison test. This, however, is the only way to generate accurate standard equivalency factors.
SBCA believes in comparative benchmark testing to establish accurate standard equivalency factors. By taking this tact, SBCA is fighting hard for a free and fair market place that has access to accurate and transparent information, which facilitates good decision making. Transparency not only serves the best interest of all of SBCA members, it benefits the entire market because it generally allows the products that are most effective at meeting market needs to win.
For more in-depth knowledge on this topic, please review this collection of published articles.
