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Re: [SEAOC] Factors of Safety: Short-Term Structures

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>William L. Polhemus, Jr. P.E. wrote:
>But what if you have a structure which, although it will have a glorious
>existence, will have a necessarily brief one?  By "brief," I'm talking
>in terms of just a few weeks!  Must you apply just as rigorous a regimen
>of safety factors to such a structure?  And if not, HOW would one 
>rationally compute the "additional" allowable?
>
>I'd love some input on this.  Thank you.

        It would seem the allowable stress increases could be used , at
least for wood structures. For example, a structure with a life span of
three months duration could be designed with a 115% stress increase (similar
to snow loads in the UBC). A structure with a lifespan of seven days could
be designed for a 125% stress increase (roof live load in the UBC). A
structure that would be up for only an hour could be designed for a 160%
stress increase (like for wind in the newer 1994 UBC)!
        Personally, I have always designed short term structures normally
knowing that I would have a higher factor of safety on them. 


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