Anchor Bolt Design ASD vs. LRFD
Anchor Bolt Design ASD vs. LRFD
(OP)
Catalogs for adhesive or mechanical anchor bolts usually give allowable and ultimate loads and their ratio is around 1:4. However ratio between nominal loads (using allowable stress design) and factored loads (using strength design) is less than 1:2. This means allowable stress design gives you anchor bolts about 2 times smaller than strength design. Am I missing something?
Thanks,
IV
Thanks,
IV






RE: Anchor Bolt Design ASD vs. LRFD
RE: Anchor Bolt Design ASD vs. LRFD
RE: Anchor Bolt Design ASD vs. LRFD
RE: Anchor Bolt Design ASD vs. LRFD
It's entirely possible to have the same reliability using factored loads and a resistance factor as with unfactored loads and a FS.
Care to elaborate? That's one of the nuttiest things I've heard in a while.
RE: Anchor Bolt Design ASD vs. LRFD
IV
RE: Anchor Bolt Design ASD vs. LRFD
The bottom line is that the ultimate loads listed in the catalog have no reduction factor placed on them. That is why you are getting such a disparity is your bolt sizes.
RE: Anchor Bolt Design ASD vs. LRFD
RE: Anchor Bolt Design ASD vs. LRFD
Correct. I would think the method is secondary and the result is primary. I guess you could probably double your Load Factors and then actually use the ultimate value and accomplish the same thing. I was just trying to point out that using traditional Load Factors you should absolutely not use the ultimate values with no reduction.
RE: Anchor Bolt Design ASD vs. LRFD
RE: Anchor Bolt Design ASD vs. LRFD
This is just like the new AISC Spec. Omega and Phi are set up to give the same overall factor of safety for a specific L/D load ratio.
For anchors, one could use this same L/D ratio and the given ASD FS and derive an equivalent phi factor. It's probably be very small, like 0.3, but I'm too lazy to calc it tonight, LOL.
RE: Anchor Bolt Design ASD vs. LRFD
I agree. I'll calc it on monday! lol
RE: Anchor Bolt Design ASD vs. LRFD
There's nothing wrong with using LRFD, but like anything else it must be done properly, not half-way and not unreasonably over or under conservative. In fact you will have a better understanding of your reliability using LRFD than you would get with ASD. There is also an ACI publication, 355, which discusses post-installed anchors and their qualifications if you are interested in some bathroom reading.
RE: Anchor Bolt Design ASD vs. LRFD
As for using factored loads with appropriate resistance factors, I was just typing philosophically. One should be able to set the resistance factor to get the same overall factor of safety.