Anchor Bolts
Anchor Bolts
(OP)
Does anyone recall what code the minimum length for anchor bolts/rods is in? I cant find it, and I know I have seen it somewhere
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RE: Anchor Bolts
RE: Anchor Bolts
RE: Anchor Bolts
RE: Anchor Bolts
DaveAtkins
RE: Anchor Bolts
RE: Anchor Bolts
The 3rd LRFD Edition refers to IBC and ASCE 7 (page 14-9)
Sections 1911 and 1912 of the 2006 IBC addresses anchorage to concrete.
RE: Anchor Bolts
RE: Anchor Bolts
DaveAtkins may be talking about a headed anchor bolt, not necessarily a straight bar with no anchorage.
RE: Anchor Bolts
RE: Anchor Bolts
Another publication by the AISC related to the design of headed anchor rods has formulae for the calculation of the embedded length that is approximately 12dia for A36 and 17dia for higher strength materials. In any event, the cone development is what determines the capacity.
If a threaded rod is used, then the end should be peened to prevent the nut from loosening during installation. In addition, the concrete should have sufficient strength to restrain the nut end.
Dik
RE: Anchor Bolts
And StructuralEIT is correct--12 times the diameter is for A36 and A307 rods.
DaveAtkins
RE: Anchor Bolts
I contend, however, that this does not comply with today's code, namely the hardest to follow mess ever pressed onto engineers, the ACI 318 Appendix D. Run through that procedure with 12d embedment, and you'll surely have less capacity than the rod's tensile capacity.
RE: Anchor Bolts
Never, but never question engineer's judgement
RE: Anchor Bolts
The unintended consequences of this unworkable mess has yet to be fully realized.
RE: Anchor Bolts
You can only do that with epoxy anchors. I don't know of a standard anchor bolt manufacturer that publishes values with tables for reductions based on spacings and edge distances. This is done with ACI Appendix D. If you only have a few anchor bolts maybe it wouldn't be a problem, but when you have a job with 100 columns and 400 anchor bolts, I imagine it can become cost prohibitive.
I have only ever used it for field fixes when the contractor mis-placed the anchor bolts.
RE: Anchor Bolts
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RE: Anchor Bolts
RE: Anchor Bolts
Dik
RE: Anchor Bolts
RE: Anchor Bolts
DaveAtkins
RE: Anchor Bolts
Dik
RE: Anchor Bolts
There would be no reason for both the ACI and the PCI to waste a bunch of money and come up with some new method if using 12d works. How does the 12d account for cracking and ductility, or the presence of reinforcement, or the variability in the strength of the materials, and other things?
RE: Anchor Bolts
It states "a 15D embedment length can be considered a satisfactory minimum embedment lenght." Then it goes on to give an equation for load capacity of an anchor bolt under simple tension. The equation is only valid for embedment lengths over 15D.
RE: Anchor Bolts
Dik
RE: Anchor Bolts
ACI approves and backs this method as does AISC. The 2nd edition of AISC's Design Guide on baseplates, which was just recently produced and is therefore the most current AISC stance on the subject, differs to ACI Appendix D for embedment calculations.
The old 12*db stuff was based on a breakout "cone" which has been replaced by the CCD method of a breakout prism in Appendix D.
I agree that 12*db might be a good minimum for anchor rod embedments on gravity columns, but it certainly is not adequate to meet today's codes to develope the tensile capacity of the rod.
RE: Anchor Bolts
For 3/4" headed bolts, I commonly use 12" min embedment; what is your suggestion?
Dik
RE: Anchor Bolts
Regardless, as noted by myself and others, this approach doesn't work today with the ACI Appendix D procedure.
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RE: Anchor Bolts
RE: Anchor Bolts
RE: Anchor Bolts
RE: Anchor Bolts
RE: Anchor Bolts
RE: Anchor Bolts
We also seem to have confusion between cast anchor rods and post installed anchors, which are both addressed though the post installed anchors are not as thoroughly reviewed and sufficent research does not exist for many types of anchors and many current anchor cannot function in cracked concrete.
Appendix D is significanyly changed from the past. It is not perfect, but it exists to fill a void and ensure the safety of the public.
As with anything, engineering judgement must be used with its application, but to call it out as a money grab and ignore it is irresponsible.
There are seminars available from both ASCE and ACI as well as others to review the changes and methodology of App D.
Additionally, Hilti and Simpson have both made efforts to provide reviews and seminars on the topic. The seminar I have attended by Simpson was very useful and remarkably unbiased. I would seacrh for their website and see if there are seminars near you.
Daniel Toon