Document: NUREG-0800
Document ID: 73747cf4-ff95-449b-b6b0-53dc0755b9e0
Document Type: srp
Title: OTHER SEISMIC CATEGORY I STRUCTURES
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1235/ML12353A382.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.8.4
CFR Part: 
CFR Title: 

Content:
e seismic design of embedded or basement walls (so-called “non-yielding” walls or “restrained” walls, that are fixed at the base, at the top, and possibly at other intermediate bracing points) should be clearly differentiated from the seismic design of earth retaining walls (so-called “yielding” or “unrestrained” walls, that are free to displace or rotate at the base). In the case of unrestrained retaining walls, the standard seismic design approach is the Mononobe-Okabe method which is based on the assumed development of the minimum active state that is modified to include, in a pseudo-static manner, the additional horizontal and vertical seismic inertial loads exerted by the soil. The active state assumption is valid in this case because a stand-alone retaining wall is free to deform away from the soil but is unlikely to deform into the soil. In the case of restrained embedded walls, the typical configuration of the problem precludes the development of the minimum active state assumption. In NPP applications, the embedded walls are not stand-alone but are part of a much larger and more massive structure that, under seismic conditions, interacts dynamically with the surrounding soil in a complex oscillatory manner. The maximum passive state condition is a potential upper bound that would correspond to the walls being pushed into the soil by the overall motion of the structure. However, the magnitude of soil deformations/strains computed from typical seismic soil-structure interaction (SSI) analysis indicates that this magnitude is much smaller than what is required to fully develop the maximum passive state. As a result, seismic design practice in the past has been based on methods that assume linear elastic or equivalent-linear elastic soil stresses/strains. It is clear that the true stress/strain state in the soil under seismic conditions is likely to deviate from the inelastic limit states discussed above. Important additional factors to consider