seismic design for retaining walls

[bjb]

The search function is down for maintenance, so I don't know if this topic has been discussed before. In the 2000 IBC, section 1622.4.2 talks about siesmic design for retaining walls, and says that the seismic forces and design methodology shall be determined in accordance with a geotechnical analysis prepared by a registered design professional. Section 1802.2.6 for SDC "C" does not require a determination of lateral pressures on basement and retaining walls from earthquake motions, but Section 1802.2.7 for SDC "D" does.

I have interpreted this to mean that for seismic design category C and better, you don't have to design basement and retaining walls for seismic forces, but for SDC "D" and worse you do. Is this how others have interpreted these sections, or is my interpretation incorrect?

 

[Qshake]

Based on what you've noted I would agree except that the walls must be able to transfer any additional lateral load (due to seismic) from the building or facility above.

Seismic Forces on retaining walls is not a complex matter. It consists of providing for the inertial effects of the wall and the soil. The latter is typically applied via Mononobe-Okabe analysis. Naturally, the location of the resultant for extreme loads is different as is the allowable bearing capacity.

For more information I suggest Foundation Engineering by Das or Soil Dyanmics by Prakash.

Regards,
Qshake

Regards,
Qshake

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[yack]

You could use the method of FEMA 356. Monobe-Okabe doesn't really apply for basement walls because they are "restrained." However, in practice it is used anyway, by default.

M.O. is an extension of Coulomb theory with an effective inertial force applied to the soil wedge. Like Bowles says, taking the Rankine failure wedge and applying the inertial force thereto is a as good a method as any.

It would be good to error on the conservative side, and take a good portion of the PGA, for your effective inertia force, since the walls are stiff.

Have fun,