Basement wall design - Load combinations 1

[Olivaw]

I know that when a basement wall is restrained by a floor slab, you have to use the K[sub]0[/sub] coefficient since the wall is subjected to at rest lateral earth pressure. I also know how to calculate the seismic lateral earth pressure as defined by my local code.

But I don't know how if I have to consider both pressures at the same time (in the same load combination). My gut feeling is telling my that during an earthquake, soil is no longer "at rest" and that soil behaviour is more complicated than can be described by K[sub]0[/sub]. Besides, it seems conservative to use them both at the same time.

How do you calculate your basement walls?

 

[TLHS]

Depends on what method you're using for earthquakes, a bunch of formulations include static loads but some fomulations separate them out or subtract the static loads back out again to give you an additional loading for earthquakes.

 

[HTURKAK]

I do not know the applicable code in your zone and no idea for the no. of basement storeys SDC for the subject bldg.
My points ,
- If you look ASCE 7 , Clause 11.8.3 Additional Geotechnical Investigation Report Requirements for Seismic Design Categories D through F. requires ,the geotechnical report shall include applicable lateral soil loads on foundations, lateral pressures on basement and
retaining walls due to earthquake motions. That is , lateral seismic soil pressures may be neglected in buildings assigned to SDC B and C.

- You may consider detailed analysis including SSI ; model the basement walls with FEM shell elements assigning passive soil springs ,
- Some codes define additional soil pressure ( Δp = 0.4* SDS *γ* Hbasement ) this pressure applied UDL to basement wall .Similar approach which you may also consider the use of Mononabe -Okabe eq.
- I will suggest you to look to the following doc.




Use it up, wear it out;
Make it do, or do without.

NEW ENGLAND MAXIM

 

[Olivaw]

My local code (Chile) is based on ASCE 7. It defines the additional soil pressure due to earthquake as an uniform load applied to the basement wall: σs = 0,3 C[sub]R[/sub] γ h A[sub]0[/sub] / g. I asked another engineer and he told me I should apply both pressures in the same load combination. I looked up another project from my office and both soil pressures (at rest and seismic) were considered in the analyisis of the basement wall.

So, I know what to do now. Thanks for the replies TLHS and HTURKAK.