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RE: Screw Factor of Safety?

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Sounds like Chapter 20 - Strength Evaluation of Existing Structures.  I'll put that one on my list of good-to-know-about's.  Generally, I see that ACI allows increases to the strength reduction factor of approximately 10% to 20%.  I suppose I could correlate that to a similar increase to what is originally a "reduction factor" of .25.  But that wouldn't even get it up to .30...
At least when I was taught LRFD, they also presented it with statistical backup to explain the logic behind the factors.  The basis (statistical?) behind the FS=4 (or 6 or 8) simply has me perplexed.

Harold Sprague <spraguehope(--nospam--at)> wrote:
I generally go to the ACI 318 for their in situ testing. It spells it out
pretty well, and accounts for safety factor, duration, etc. I am on the
road in San Fran so I can't tell you which chapter.

Harold Sprague

>From: Jim Wilson
>To: seaint(--nospam--at)
>Subject: Screw Factor of Safety?
>Date: Mon, 30 Aug 2004 14:37:28 -0700 (PDT)
>Most catalog fasteners (i.e. self-drilling screws, epansion anchors, etc.)
>have a factor of safety of 4(or higher) for design. Is there a different
>factor of safety when considered during field testing?
>Presumably, the safety factor is so high so that it accounts for the
>differences between perfect world testing and actual field conditions.
>What if the testing is done on the actual field conditions? Shouldn't the
>safety factor be lower since the tested value has already taken site
>conditions into consideration?
>Surprise, surprise, another contractor mishap I am expected to bless...
>Jim Wilson, PE
>Stroudsburg, PA
>Do you Yahoo!?
>Win 1 of 4,000 free domain names from Yahoo! Enter now.

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