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Re: More questions about rigid plywood Diaphragms

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At 11:05 PM 6/27/99 EDT, Dennis Wish wrote:
>Thanks Ray, we seem to agree.
>Now to carry it a step further, since there is no adequate way to evalute the 
>rigidity of this type of diaphragm, would there be a liablity to the engineer 
>that uses professional judgment to evaluate the condition as flexible 
>inasmuch as the methodology presented in the code would not be adequate?
>
>Dennis
---------------

C.G.:
As to "liability", the answer in my encounters is found not in the soundness
of your judgment, or in the strength of your personal convictions in the
technical matter at hand, or in getting a building permit on it, but rather
in how persuasive is an "expert" who says you got it wrong and violated
either a code provision or a standard of care.

Persuasive to whom, then? To the arbitrator, or to the jury, or to the judge
if there is no jury, or to your insurance company (because it costs a lot
more to go to trial and maybe not win real big than to pay to settle and be
done with it.) 

In the further peril where someone complained to the PE Board and your
license is at stake, the board obtains its own expert from a list, and
relies almost totally on that person. None of the PE Board members are
consulted, ever. If that "expert" (ie, any PE in your branch, and perhaps
far less experienced than you) is reasonably persuasive to the board's
enforcement staffers and to a career deputy attorney general, the
prosecution is on. Then the person to whom the persuasiveness counts is the
hearing officer, an administrative law judge from the Office of
Administrative Hearings. (I will be testifying again as a defense expert in
such a hearing later this week, over a minor residential consulting
engagement; can't say any more on it at this time.)

Who's missing in this list of who gets persuaded? The Building Official.
That person's role is long since over with. The building permit got issued
on the basis of the building official's decision, but your liability depends
on how a hostile, paid expert persuades some other decision-maker who isn't
bound by what the building official accepted. 

This is why Ben Yousefi's enlightened but limited views of 6/1/99 on the
commendably flexible role of the plans reviewer at his San Jose building
department nevertheless miss the mark when it comes to the liability and
license perils faced by design engineers at the hands of other code
interpreters later. He said, 

>My final comment is regarding code language and how we interpret it. Codes 
>are written as general guidelines that set basic criteria for how things 
>should be designed. Thus the "shall" language addresses only the clear cut 
>situations without considering other relevant facts.... 
>
>Therefore, the judgment of the engineer of the record in conjunction with the 
>code regulating authority is of utmost importance in order to implement a 
>sound application of the code. 

Right, except for the unknown, unseen "expert" lurking like a troll under
the bridge, and whose expectations on strict code compliance far exceed
those the friendly code agency overtly agreed to, or merely took no
exception to. Ben's code change indeed made a flexible provision rigid (puns
unavoidable) even though Ben personally favors staying flexible. My
unregretted 6/1 pie throwing was for the hypocrisy of newly creating a rigid
code rule the proponent himself intends to waive enforcement of, but that
others later will sue and prosecute the same design engineers for violating.  

Back to gable diaphragms:

In a previous posting I said that expert testifiers are apt to make the most
outlandish and preposterous claims as to what someone else did wrong. No
kidding. One commonly overdone claim of dereliction is that no calculations
were performed by the accused engineer as backing for a chosen design
assumption or methodology. Sometimes however the burden of showing that
calcs weren't needed can fall fairly on the designer who chose not to. 

Dennis's previously posted arguments:

>I would argue that any scissor truss or vaulted ceiling which exceeds a 
>3:12 slope could not be designed as rigid by nature of it's performance. 
>
>I might be more inclined to accept a minimally sloped roof (1/4:12) as 
>having greater ridgidity - however, I am still reluctant to treat it as a 
>rigid diaphragm by nature of the quality of construction unknowns.
>
>I don't want to waste time working through the analysis for rigidity if my 
>professional judgment tells me that the calculations are not adequate to 
>determine deflection of a pitched roof.

....seem not to reflect the results of calculations, either custom for the
project or a stock file calculation made to substantiate or refute the above
stated conclusions. I am not going to venture whether I agree with these
premises because I have not yet tackled the strength of materials and
free-body diagram problem that the matter can easily be rendered into. But I
would have little trouble testifying that it is improper to jump to those
code-defying conclusions by feel or by guesswork, when it can be checked out
with traditional, simple tools of analysis. In other words, engineers should
resort to doing some engineering as backing for those engineering opinions
they hold that aren't well established and uncontroversial. That "rational
analysis" provision in the front of Chap 16 is about this.

Same goes for code provision writers, but even more so: Where's your
rational analysis for that restriction you cause everyone to be bound by?
Or is guesswork without "wasting time working through the analysis"
peculiarly OK in the codewriting world, where there's no liability risk?
Save your own time and waste everyone else's later? And waste their money in
legal defense efforts?

Charles O. Greenlaw, SE     Sacramento CA