Why Scientific Truss Weather Testing Has Value for CMs

Originally published by the following source: SBC MagazineDecember 10, 2018
by Evan Protexter, P.E. and Kirk Grundal, P.E.

   

Step one of the scientific method is to ask a question. In the article Weathering Trusses, Exposing the Effect of Time and Nature, we took the first step and asked how weather might impact the performance of trusses including but not limited to truss structural performance characteristics. Now we can move on to step two. This involves doing background research to determine if performing testing is necessary, or if the information sought is already available. Given the fact that trusses have been part of the building industry since the 1950s, it is reasonable to believe that some effort has been made to learn about trusses exposed to the elements.

The most critical part of literature research is determining whether the research answers the initial question in the first place. There are plenty of resources on construction using metal plate connected wood trusses: Forest Products Laboratory, TPI 1 and SBCA to name three.

While all data can be useful, all reports that have been discovered so far have left the question of a truss’s structural integrity due to extensive weathering unanswered.

While there have been no reports found that explicitly answer the aforementioned question regarding truss performance, a number of reports regarding truss plate movement due to moisture and weathering have been helpful.

One example of this is an Alpine internal study in which joint samples were exposed to weather under various storage conditions and tested for lateral resistance. This information increases our knowledge of plate movement and is being used as a reference.

The weathering testing that is taking place and is covered through this series of articles is critical to answer the questions that component manufacturers have about trusses that have been left outside. By performing testing that is directed at truss performance and not just one piece of the weathering puzzle, the industry will be able to say with confidence whether trusses left outside will perform as initially expected.

For additional information, please review the following articles and internet links:

  1. SBCA Quality Control
  2. Structural Building Components Research Institute
  3. Best Way to Frame
  4. SBC Mag articles and news items
    1. SBCA Testing Impact of Weather on Trusses
    2. Weathering Trusses, Exposing the Effect of Time and Nature
    3. How Long is Too Long?
  5. Topical library articles
  6. Durability articles
    1.  Do You Know What It Takes to Pick the Perfect Plate
    2.  Preemptive Design
  7. https://www.fpl.fs.fed.us/research/units/4723.php