At this time, I am not sure how I will design wood while waiting on the possible new design values. There are several issues to consider before making this decision.This was a short and quick answer to a complex problem. I have two new wood projects on my desk, including a multi-story apartment building, that will give me a chance to create and implement solutions for ensuring an appropriate design. I will post about my findings in the next few weeks as I complete the projects.
First, I have yet to see the actual proposed new design values. While I do not doubt the testing, I would like to see the test data. Researchers at
have conducted some tests that show a decrease in lumber strength but not enough to justify the amount of design value reduction proposed by SPIB. Mississippi State
Second, while the proposed new values cover each size of southern pine, only 2x4's have been tested. I do not think we can assume a correlation between the design values of each size based on the In-Grade testing performed 20 years ago. Too much has changed in the timber industry.
I think the easiest thing to do is limit the stress ratio of members we design to maybe 0.80 instead of 1.0. This would be easier than trying to adjust design values at this time and it may not make a significant difference in the overall design.
Also, I have requested a copy of the SPIB proposal. The recent comments from the SLMA has a link to request the proposal for those who are interested.
Another good commentary regarding the industry's stance (or lack thereof) on what to do between now and January 5th when the ALSC rules on the design changes is here.