Seismic Design of Retaining Walls AASHTO

[GeoGeoGeo]

I am desiginig Retaining walls. Which pseudostatic force shall I use the basic acceleration in rock or the máximum acceleration of the spectrum.
Does AASHTO include any reduction of this force/acceleration?

Kind regards

 

[BridgeSmith]

Per the 9th Ed., anyway, it appears you would use the max acceleration, and if you're on rock, you may have to increase it beyond that.

11.6.5.2—Calculation of Seismic Acceleration Coefficients for Wall Design

11.6.5.2.1—Characterization of Acceleration at Wall Base

The seismic horizontal acceleration coefficient, kh, for computation of seismic lateral earth pressures and loads shall be determined on the basis of the PGA at the ground surface (i.e., kh0 = Fpga PGA = As, where kh0 is the seismic horizontal acceleration coefficient assuming zero
wall displacement occurs). The acceleration coefficient determined at the original ground surface should be considered to be the acceleration coefficient acting at the wall base. For walls founded on Site Class A or B soil (hard or soft rock), kh0 shall be based on 1.2 times the site adjusted
peak ground acceleration coefficient (i.e., kh0 = 1.2FpgaPGA).

 

[BridgeSmith]

Designing the wall to survive that acceleration, of course, is only necessary if the expected movement of the wall would constitute an unacceptable failure of the wall. Few of our walls would present a life-safety hazard, or make an essential corridor impassable, if they were to experience the displacements expected during the design seismic event, so we generally don't design them to withstand for those loads.