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# calculating kh from 0.4*SDS

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## calculating kh from 0.4*SDS

(OP)
[highlight #EF2929]thread507-418397: Seismic Lateral Earth Pressure for Retaining Wall Design

Dear Engineers, I am designing a retaining wall, I need to consider seismic load.

From FEMA 450, calculate the Kh factor. as Kh = Sds/2.5. My question is about ss value, it is given in % of g. for example for Jeddah city it is about 35 (not divided by 100 to become 0.35).

For calculating SMS = Fa*SS, shall I consider the ss as (35/100)*9.81 = 3.4335 or just 35 or 0.35 only.

I searched but I could not find an example to calculate kh.

Thank you

### RE: calculating kh from 0.4*SDS

You may use 35% (of g) or 0.35

I've always seen examples using 0.35 to avoid later confusion in the calculations, but I suppose the percentage could be carried through.

----
just call me Lo.

### RE: calculating kh from 0.4*SDS

(OP)
Yes, I also see examples using 0.35, but are them for calculating kh ?. I could not find an example for calculating kh specifically.

### RE: calculating kh from 0.4*SDS

(OP)
no more answers ?

### RE: calculating kh from 0.4*SDS

I think seismic design of retaining walls is a bit suspect and usually ends up being way over designed. When I do them, I would start with Monobe-Okabe.

An online reference for some of the seismic calculations of a retaining wall:
RetainPro

I really think the Retain Pro manual is the best reference for retaining wall design. It goes into a lot of little details about retaining wall design and gives a pretty good explanation of seismic.

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