Seismic Load on Basement Wall 1

[SteveGregory]

Does the earth have a seismic mass associated with it that will add an out of plane load to a basement wall? Normally, we design basement walls for "at rest" earth pressure. How about a seismic load on the wall?

another question... For a building with 1 or 2 stories below grade or partially below grade, can passive pressure in the soil be utilized to resist lateral loads generated by earthquakes?

We use ASCE 7-05 and most of the buildings that we design are in Seismic Design Category B or C.

 

[JedClampett]

We usually ask for the Geotechnical Engineer to provide seismic soil loads as part of their report.
As far as using passive pressures to resist seismic, you're asking the building to move quite a bit to develop the passive pressure. That might be undesirable.

 

[SteveGregory]

Thanks Jed,
I found this 2006 paper that suggests not including a seismic lateral load from the soil mass on basement walls in most cases. Thoughts?

http://www.ce.berkeley.edu/~lalatik/hudson.pdf

 

[ChipB]

I believe you want the Kh coefficient for the soil.

As far as using passive on the other side, absolutely NOT!
Keep in mind, seismic forces go from the foundation, UP the structure. The soil/foundation interaction is what is putting the load into your structure. Besides, if your soil has liquified on one side, it's likely done the same on the other.

 

[msucog]

agreed. no passive. it's all moving.

as far as that link, i have my problems with some of the things mentioned in there but i'll refrain from getting on my high horse tonight.

see if this helps

http://www.bssconline.org/2nd09MOballot/Part3/TS-3 proposal 3-6_Geologic Hazards.pdf

 

[ErnestoD]

I strongly recommend you to use the mononobe-okabe method. There are many papers in the net regarding this method.

Regarding to your second question, what you can do is compute for the horizontal spring stiffnes of the soil. This will vary with depth. The deeper, the stiffer your spring support. Refer to "Foundation design and analysis" by bowles.

 

[SteveGregory]

Thanks everyone for your help.

Based on ASCE 7-05 11.8.3, it looks like seismic lateral earth pressures are not an issue for SDC A through C.

msucog, if I understand the IBC paper correctly, the M-O method should be used for cantilever retaining walls (yielding)and the Wood method should be used for basement retaining walls (non-yielding).

 

[msucog]

i don't see why M-O wouldn't be okay for both. wood may be "better" for basement walls but i don't see that M-O is prohibited. for M-O the reduction in pga is different depending on yielding or non-yielding. the link you posted suggests using 1/3 pga. the proposed code link i posted doesn't agree with this.

for the better SDC, the seismic loading should be rather trivial for many/most situations. you could check it by looking at pga for the different SDC. pga = Sds/2.5 which works out to be near 0.1g or less for many locations. this tends to correspond to the amax from the old aashto maps from what i've seen in my area. so for SDC A, Sds is very low which means pga is very low which means the seismic loading is small. i would think that SDC C calcs might be a little more critical depending on the embeddment depth in to the ground. for SDC A, seismic loading might be disregarded all together.

as for 11.8.3, i don't think it's saying it's a non-issue. i think it's saying that for SDC D, it must be calculated (since seismic forces are amplified more in crappy soils). however, for SDC A-C, it is up to the engineer to decide if it's worth checking.

i'm no seismic guru but that's my take on it.

 

[jechols]

I have a project with soil bermed up on two opposing sides of a building all the way to the roof (1 story about 20' tall). Would you consider the soil when determining base shear?

Thanks,
j