Timber pole retaining wall

[L0k]

Hi, I am designing a timber pole retaining wall. I stuck at what retained height I have to apply the earthquake loads.
The other query is whether I have to use 100% live load surcharge or less.
If you have any references for these queries, it is much appreciated. Thanks.

 

[Doctormo]

There are some newer conflicting theories on the point of application of seismic loads on retaining walls. See AASHTO LRFD 2015-16 for discussion.

AASHTO now just calculates a total load (Pae from Mononobe-Okabe) and applies it at 1/3 of the design height with some discussion that it may be between 1/3 and 1/2 of the design height. The older AASHTO code broke the loads into static and dynamic components and applied at different locations.

There has also been some conflicts with the application of live load and how much. For years, live load was ignored when doing a seismic retaining wall analysis per AASHTO with current AASHTO LRFD suggesting that a partial load factor of 0.50 may be appropriate vs. the 1.75 load factor used in the static analysis. It is accounted for in some manner this way.

If I had to make a guess, I would apply the earthquake load, if separate from static loads, at 1/2 of the retained height and then make a judgement call of whether to include live load or not. It really has more to do with which code or design procedures one is following.

 

[KootK]

For non-tranportation walls, I've been using Los Angeles' residential guideline. NZ has some good docs too. I suspect that the flexibility inherent in a timber system would change things a bit. I know of no reference for that however.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[msquared48]

If the surcharge is from a building, I would say include it with the seismic load.

If the surcharge is from traffic, I would say not to include it with the seismic load.

It depends on whether or not the surcharge is permanent.

Mike McCann, PE, SE (WA)

 

[L0k]

Thanks Doctormo, I do not have your ref. AASHTO LRFD 2015-16 yet, but I am using Ko instead of a classic Mononobe-Okabe and using DPae= 0.75a.g.h2 (Wood & Elm, 1990)
While surcharge/live load is applied 50%.
Thanks KootK, now I have a guidance to use 6ft (1.83m) retained height to start applying the seismic loads.
Thanks msquared48, I agree to apply 100% for building and zero for traffic.
Thanks all for your suggestions.