Retaining wall displacement
Retaining wall displacement
(OP)
Hi, does anybody have references on how to determine the amount of displacement of a retaining wall due to seismic forces? I am understand that there are FEM techniques but this is for a preliminary study so I am just looking for something that can be done manually. Thanks for your input.





RE: Retaining wall displacement
See NCHRP Report 611 for a semi-readable explanantion. See Prof Bray (UCB) and Kramer (UW) for a slightly more high-powered approach.
For simplified analysis (done by almost everyone except PhDs), there is a tradeoff between the pseudo-acceleration used in the design lateral forces and the resulting permanent wall displacement (via Newmark charts / equations).
For design acceleration = 0.5A, where A is the peak ground acceleration (g), horiz wall displ = 10*A (inches). So for A = 0.5g, displ = 5". Seems a bit high to me, but that's what the smart guys say.
I think AASHTO commentary says expect 2" to 4" displ if using reduced (0.5A) accelerations. Seems like a good rule of thumb in the absence of other recommendations.
Even less well defined and understood is the permanent wall tilt.
RE: Retaining wall displacement
Also, the code that I am using for my DoD project, indicates that the seismic coefficient should be Ss/2.5, which is actually my PGA. I found it high since as you mentioned most of the references suggest seismic coefficients less than the PGA.
Thanks again...
RE: Retaining wall displacement
Richards & Elms has some good discussion on the concepts of the seismic event and structures. You would really have to know the seismic event profile to predict the movement thus one would have to acquire a lot of information to make an educated prediction then you would still probably not be correct, similar to settlement estimates that are routinely off by quite a bit.
You could design a wall for the full PGA and As and would probably still get seismic movement even though this would be considered the "no movement" situation. If the structure is extremely stiff to reduce movement, you would be designing for Ko vs. Ka conditions so this comes into play as well.
To me it is more of a minimal movement vs. significant movement situation where you can design for one or the other with the actual movement being somewhat indeterminate.
RE: Retaining wall displacement
RE: Retaining wall displacement
This is pretty rough and would not tell you how much a wall might lean out or how much settlement or cracking you might get behind the wall after movement but it is better than nothing I suppose.
RE: Retaining wall displacement