ASCE 7-05 12.4.2.2 vertical seismic load effect on foundation design

[Oversee]

Ev=0 is required for those load combinations containing Eh-Ev when checking “soil-structure interface of foundations”. I am not sure about this terminology at all. Does soil-structure interface demand cover all checks such as ground bearing, overturning and sliding?

My second question is: why Ev=0 is not applicable for E=E+Ev. Or, what are the design implications in terms of signs of Ev (seismic uplift force).

I wish to thank you all in advance.

 

[JoshPlumSE]

I'm not familiar with that language in the code (and am too lazy to look it up right now).

But, my take on it is that the Ev doesn't really need to be considered for cases where you're looking at 0.6*DL for overturning / uplift and such for the foundation. The DL really is artificially reduced in those cases (to provide a 1.5 overturning safety factor).

It would seem to be overkill to require even more uplift / overturning for those seismic cases. In fact, I believe the 1997 UBC had a restriction that the vertical component of earthquake did not need to be considered at all for ASD load combinations.

 

[weab]

Not much to add except this. The 1997 code says that Ev for ASD is 0 because the DL factor is relatively high (0.9?). It is assumed that any vertical load is included.