Anchor Bolt Design - Load Combinaitons

[htex404040]

Hello all,

I am in the process of designing anchor bolts for tension (the shear will be resisted by base friction), I am only looking at bolt strength, not concrete at this point. For referance I am using "Wind Loads and Anchor Bolt Design for Petrochemical Facilities". In section 3.6.1.1 (anchor bolt section) they are checking combined tension and shear and they show the check using Ultimate Strength Design (part a) and using Allowable Stress Design (part b). My worst case tension loads for each case would be 0.9DL+1.6WL and 0.6DL+1.0WL for Strength Design and Allowable Stress Design respectively.

I am only looking to size the bolt diameter for tension, again not looking at the concrete, what load combination should I use? One or the other, or check both and take the worst case scenario.

Thank you in advance for your help.

 

[UcfSE]

You should use the method that is consistent with how you designed the rest of the structure as much as possible.

 

[htex404040]

I have not been responsible for the entire structures design, I am solely looking sizing anchor bolts. I just didn't know which design method was the correct one to use in this situation.

 

[jdonville]

htex,

I would check both, keeping in mind that the concrete should fail before the anchor in the ultimate case.

Jeff

 

[VoyageofDiscovery]

jdonville,

Absolutely NOT, the anchor bolt MUST yield first, otherwise one gets a catastrophic failure. Ultimate theory depends on yielding.

VOD

 

[graybeach]

htex404040,
You should check all load combinations. Sometimes with anchor bolts, it is hard to tell which combination controls just by inspection. I always make a table with the resultant forces and associated factors from all design combinations. This way design calculations show that all combinations were checked and which combination controls.

 

[JKW05]

I believe the question in the OP isn't well-phrased. The load combinations listed are for two different design methods, with each of the shown combinations representing the same or, at least a similar condition (reduced DL with full WL).

So if the question is: Which design method should I use, then I would say either can be used, however it appears that ACI Appendix D is geared toward LRFD.

If the question is indeed, "Which combination should I use", you will need to check all of the combinations in ASCE 7 that is consistent with the design method you choose.

 

[htex404040]

JKW05,

Thank you for the clarification, I was indeed asking which design method I should use (ultimate strength design or allowable stress design) to size my bolt for tension. The two load combinations I was referring to are, like you said, the reduced DL and full/increased wind load combinations from each design method. I am looking at these two only in this case in order to size my bolts for tension.

From what I've read above it sounds like either way would be sufficient, in which case I suppose I should look at both design methods seperately and compare to find which one gives me the worst case. Or can I just pick one and go with that?

 

[JKW05]

You can choose which design method to use. But as UcfSE said, it is preferable to be consistent with the design used for the rest of the structure. If you come up with a significant difference in bolt size for using the two methods, there is probably something wrong (e.g. 1/4" dia with LRFD and 1" with ASD).

It is unfortunate that you say "I am only looking to size the bolt diameter for tension, again not looking at the concrete". This seems to be the standard for Metal Building companies, who wash their hands of any consideration for the foundation. I don't mean design, I mean coordination with the foundation elements/anchorage. The size, spacing and locations of the bolts with respect to the supporting concrete pier or footing must be considered to properly size the anchorage.

See this thread....

http://www.eng-tips.com/viewthread.cfm?qid=204844&page=1