aci 318 appendix d, anchorage for simpson shearwalls

huangyhg

aci 318 appendix d, anchorage for simpson shearwalls
hello,
i have been reading all the threads that i can regarding the aci 318 appendix d and the calculation for anchor bolt capacity placed in concrete.  i just recently performed a calculation based on a simpson shearwall that is sw18x9 and is resisting a relatively minor asd load of 420 lb, when translated to lrfd and multiplied by the 2.5 factor (assuming concrete failure) becomes about 1470 lb.  in deterimining the uplift load based on the 9 ft height and 1.5' width, the tension load on the anchor at each side becomes quite large, about 8830 lbs.
it appears that the only way to get the anchorage to work is to insure that ductile failure of either the anchor bolt or holdown occurs rather than the concrete failure.
in this case i was prepared to use a 12"x 28" deep footing because simpson suggests using the sstb28 anchor bolt, with just under 25" of embedment.
assume
c1 = 2 inches.  
hef = 8*do (can i use the full embedment or is this the limiting factor
single anchor
it appears based on all the different failure modes, that pullout governed by 0.9f'cehdo is the lowest load based on the concrete compressive strength (2500 psi), anchor bolt diameter (7/8"), and eh which is apparently between 3 and 4.5 times the bolt diameter as well as the factor yc,p (1.4 i assumed non cracked at service loads).
by using the previous equation and taking the additional 0.75 required by the cbc20007 (d3.3.3).  i get that a 1.25" diameter anchor bolt would be required for this load.
that seems a little crazy for this situation.  can somebody tell me if i have incorrect calculations or if they have performed the calculations for simpson shear walls and were able to come up with a different answer?
thanks for your help!
structeng13

call the simpson folks directly and ask one of their engineers.  they are typically willing to sort through calculations and help understand where their numbers come from.