Need Clarification

[msquared48]

I have seen a few soils reports lately where the earthquake lateral load is specified as E = 8H.

Does this mean that the triangular EFP is replaced by a rectangular 8H pressure, or combined with it? Or is the 8H pressure an additional triangular distribution to be combined with the EFP? Seems like it would vary too as does the EFP when applied to yielding and non-yielding walls, but the equation and soils reports do not reflect this. Also seems like the 8H value should be limited to a depth as for 20 foot walls, this could increase the lateral load to the wall by a factor of 1.5 to 2 times.

What am I missing here?

Mike McCann
MMC Engineering

 

[Erdbau]

8H seems in the right ballpark of an inverted triangular pressure distribution (8H psf at the top, 0 at the bottom) that is added to the EFP, coming from a Mononobe-Okabe solution for earthquake pressure. You are right, the pressure should be greater for a non-yielding wall. I believe AASHTO recommends using 0.5 times PGA for an acceleration coefficient for a yielding wall, and 1.5 times PGA for a non-yielding wall. Depends on the state code, as well. There might be one value regardless of movement.

But, as I'm sure you're aware, it's hard to say for certain if the reports just give you a load and don't tell you how and where to apply it.

 

[jasperrupp]

It’s hard to give you an accurate answer with only the information you provided. But from what I can tell, Erdbau is right.