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Re: Break Away Structures

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Sir or Madam,

        The only experience I have had with "break away" structures has involved
explosion relief panels for industrial buildings and then only about two cases.

        The requirement for this is to select the fasteners and size the openings
such that the safe design capacity of the fasteners is high enough to resist the
wind loading and the ultimate strength of the fasteners in low enough that the
"design blast" pressure will blow out the panel.  Of course safety chains are
required to prevent the (now loose) panel from flying away and creating its own
hazard.

        Usually it is necessary to negotiate the magnitude of the "design blast"
pressure with the owner (or end user) since the difference between safe load and
ultimate load for the fasteners doesn't necessarily match the owner's desires.

        These panels typically pose a maintenance problem since determining the
magnitude of the wind loading is not an exact science (at least not for practical
structural engineers; it may well be for aeronautical engineers who want to spend a
lot of engineering time on this) and over design is not an option.

        I suspect that the major problem in designing any "break away" structure
you may work on will be in managing the difference between safe working load and
break away load.  Over design will not be an option either for working or for break
away conditions.

        You may have to lower the usual "safety factors" used in structural
design.  But then, safety factors are nothing but ignorance factors used to account
for unknown information and simplified engineering procedures.  You can safely
lower these safety factors if you use a lot more than usual design engineering
effort and (especially) a lot more quality control supervision.

        Be sure you have a good contract and insurance.  Pay particular attention
to the details dealing with your financial responsibility for the work!

        I hope some of the above is helpful to you.

        Good luck with the project; it should be a great experience.

Regards,

H. Daryl Richardson

ggobo(--nospam--at)att.net wrote:

> Does anywone know what the requirements are for "break away" structures? For
> example: A bridge over an existing waterway. Is there ever a situation where
> you would want to design a break away structure? If so, what are the guidlines?
>
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