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Re: We're Not Getting Older, We're Getting DUMBER

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Gary,

You mentioned that the failure was likely due to over estimation of dead loads (balancing loads). That sounds like a lack of application of the 0.6 dead load factor where the dead load helps you, a failure in judgment, a misunderstanding of the codes, or some combination thereof. I'd hate to think that the reason for switching is so that we can ignore mechanics in favor of a more complicated spreadsheet.

For the record, there is a slight difference in the codes - under ASD, the dead load is factored at 0.6, whereas in LRFD, the dead load has a relative factor of 0.56. So there is a small, potentially non-conservative difference, if you decide to overestimate your weight, and then carry that weight through to your load cases where weight helps the structures stability. (In hand calcs, I usually carry a heavy and a light DL number - i.e. with & without interior partitions)

Jordan

Gary Hodgson & Associates wrote:

Chris,
I recently quoted a transmission tower that failed when
designed by ASD where they say it probably would not
have failed if designed by LFRD.  My source (they) was
Mike Gilmor at the Canadian Institute of Steel
Construction-phone 416-491-4552.
Gary


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