huangyhg

asce 7-05 seismic provision
i don't understand the thought process of splitting the seismic load effect "e" into two components (eh and ev). i have calculated the eh and ev components but am trying to grasp how to use them in the load combinations.
in my structure, i have assumed the ev to be negative (uplift). no particular reason, just the way i chose to think about it. the eh is also negative due to customer sign conventions. with all that said....
section 12.4.2 states:
e = eh + ev in asd load combinations 5 and 6
e = eh - ev in asd load combination 8
in my case, looking at e = eh + ev. do i add the two loads and then substitute the e into the load combination or should i use eh and ev in the load combination so that the result is additive? if i add the two loads, which direction is e applied.
any help would be great.
ryan
it might be the primary and secondary wave of a typical earthquake where the primary one is essentially a compression wave and the secondary one is one of vertical translation.
dik
rgerk,
check out these threads that discuss the vertical component effect from seismic:
ryan - per the two referenced threads above - the key to re
jae,
thanks for the information. i believe i understand it. let me recap my thinking now.
considering e = eh + ev:
load comb 5 - d + h + f + 0.7eh + 0.7ev
load comb 6 - d + h + f + 0.75(0.7eh + 0.7ev) + 0.75l + 0.75(lr or s or r)
considering e = eh - ev:
load comb 8 - 0.6d + 0.7eh + h
in load combination 8, i wouldn't considered the load effects from the vertical seismic ev.
does this make sense?
ryan
i think the negative for the ev is intended to suggest that the vertical component of the seismic effect e should be taken upward to make the overturning check more conservative.

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