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Re: structures & ethics

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I would recommend:

1. Check with the building department and/or building owner to see if original plans are available.  Sometimes, substantial changes have been made over time which could effect the loadings.  

2. Get a quick peer review from the list on your purlin calculations by posting a more complete description of the materials supported and your estimated loads and the sizes of purlins and the material properties you assumed(the information you posted is pretty sketchy for the purlins). The calculation is very straightforward and takes only minutes.  From the glulam size, cantilever and common bending strengths available in the 1970's, it appears you may have a dead load of about 19 psf if they were designed to the limit. If so, that would require some rather hefty purlins.  Also, have you attempted to visually determine the approximate grade of the purlins?

2. If the condition is as bad as you indicate, sit down with the client and explain what you found and the potential consequences (wood can let go over time either in a brittle manner or by cracking and sagging [that is why the NDS specifies a Cd factor for loading duration}). The former is definitely a life safety issue.

3. If you judge that, in your professional opinion, the structure is a life safety problem, you need to consult with the local building official. Somehow I can just hear the opposing attorney asking, "You knew it was going to fall down and you didn't do anything?"

Bill Cain, SE
Berkeley CA

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