Seismic Force for a gravity wall in AASHTO

[Awre]

Hi,

I am calculating the seismic force on a gravity wall per AASHTO.
The concentrated dead load surcharge pressure distribution is not clear (to me!).
How can I estimate the maximum, and minimum pressure values for the trapezoid to calculate Fp?
Also, is Kaf is the same as Ka utilizing Coulomb, etc.? or is it different? I do not see how Kaf is calculated...

Lastly, does the diagram imply that only dead weight to be considered, and no live loads etc?

I am attaching the figure from AASHTO... I appreciate any help... Thanks

 

[geotechguy1]

The seismic load on a retaining wall is generally calculated using 'KAE' which is active earth pressure coefficient for the seismic case calculated using mononobe okabe. Check out NCHRP Report 611 section 7.6 and 7.7. From looking at AASHTO references Kaf seems to be Ka for fill.

 

[Waxwing]

The shape of surcharge distributions vary depending on the model, wall height, type of wall, and type of load. Study up and contact the geotech. Get a copy of the Bowles textbook.

The MO equation mentioned by geotechguy1 (if I remember correctly) is the same as Coulomb theory, just adds an acceleration force to the active wedge.

The load combinations are tabulated in the LRFD code. Make sure to check if they have been amended by the state you are working in.