anchor bolt design question

huangyhg

anchor bolt design question
when designing anchor bolts for tanks and silos on braced legs, asce 7-05 states that the element design force is to be multiplied by omega (asce 7-05, 15.7.3 (a)) for anchorage.  thus, in addition to using factored loads for concrete design, and a .75 reduction on your allowables for anchorage design (aci app d, rd.3.3) in high seismic areas, you are then multiplying your loads by omega (2 in this case) for design of your anchor bolts.  following this method, we end up having to use substantially larger anchor bolts and mat thicknesses than what we used in the past.  we have discussed using service loads multiplied by omega for design of the anchorage using aci appendix d, instead of factored loads.  has anybody else had experience with this?  does this sound unreasonable?
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appendix d is for plain concrete.  you can use the reinforcing in your footing to help with anchorage.  there was a good thread and article posted on this recently, i would do a search on here.
under the "aci (concrete) code issues" forum - check the thread entitled "aci-05 app d anchor bolt supplemental reinforcement".  it is about the third one down on the page.  
cessna98j ,
i feel that all these factors are being introduce to make sure there is no brittle failue due to failure of bolts.
structuraleit - thanks for the link, that article looks to be very useful.  we use that exact method when designing pedestals for tension & shear.  however, the "beam" method for spread footings looks to be a better approach to keeping designs a little more economical.  do you all think that with these methods then, which take into account the strength of the reinforcing steel, that the omega factor is still applicable in addition to everything else?