seismic load combination
 

seismic load combination
hi,
i was checking cl 12.4.2.3 for seismic load combinations, in which 0.2sds is used to account for the seismic load in vertical direction. for rest of the horizontal seismic loads , one can use 100% in x dir and 30% in z dir (seismic design cat d).
what if 100% is in the vertical direction, should it then be 100%vertical + 30% hor-x + 30%hor-z
i have seen this combination to be used in some other design offices, but where is the ref in code.

100% vert + 30%x + 30%z?? no.
the primary seismic is always either x or z. the vertical is just an added seismic effect that accompanies the x or z.
i've seen something like this before and i think it could possibly have come from asce 4 for "seismic analysis of safety-related nuclear structures" although i can't find it in the spec now. it might have been in other contract specs.
regards,
-mike
thanks jae & mikee,
from this discussion now i can remember that the 100% vertical seismic effect was really mentioned in the nuclear dbr.
so the eccence is vertical has to be 20% if i am using asce7 load comb.