What Can We Tell From This Photo? (Case Study 18)

Posted by in Case Studies, Wood | April 29, 2019

One of my favorite sayings is, “When something doesn’t look quite right, it probably isn’t.”

This maxim has served me well, both professionally and personally.  Some would probably call it “instinct” or “the subconscious mind.”  Whatever it is called it processes a quick analysis of the conditions, situation, or circumstances and comes to the conclusion that something is wrong. 

It reminds me of the game we played as a child or watched on Sesame Street, “One of these things doesn’t belong here.” 

Well, let’s play that game with the following photograph.  What doesn’t look right, besides the trusses being collapsed onto the floor?  After giving it some thought you can read my list provided after the photograph.

Truss collapse viewed from the attic.

Here’s my list:

  1. Despite the roof framing being in the fallen state, the individual trusses and the straight bracing are easily and clearly visible.  Thus, something must be missing or inadequate. That something is truss bracing.
  2. The 2×4 braces are not lapped across two trusses.
  3. Where is the diagonal bracing for the straight bracing?
  4. Where are the protruding nail shanks where the purlins have separated from the top chord?
  5. The trusses fell as a unit indicating that the failure was probably widespread and not a localized issue in one truss.
  6. The vertical separations in the truss members indicate that that the trusses fell out from under the roof deck as opposed to being pushed down by an excessive weight on the roof deck above.   

If you have additional observations, please send me an email.

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