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Re: SEISMIC LOADING ON BASEMENT WALLS

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Gary,

ASCE7-05, Section 15.6.1 Earth-retaining Structures states: "The lateral earth pressures due to earthquake ground motions shall be determined in accordance with Section 11.8.3 for Seismic Design Categories B, C, D, and F with a geotechnical analysis prepared by a registered design professional."  The section goes further into a brief discussion about the yielding and non-yielding retaining walls.

The 2007 AASHTO Bridge Design Specification addresses the issue in the appendix to Chapter 11  Seismic Design of Abutments and Gravity Retaining Structures.  The appendix cites multiple cases of the seismic failures of abutments and retaining walls, provides recommendations for the design based on Mononobe-Okabe, and points out the limitations of such approach. 

The 2007 California Building Code Section 1806A.1 states that "Retaining walls higher than 12 feet as measured from the top of the foundation, shall be designed to resist the additional earth pressure caused by seismic ground shaking."  Although this section provides some guidance toward the design, all that is happily skipped in the design of retaining walls lower than 12 feet - meaning that such design does not, in most cases, consider seismic loading.  I never saw a documented earthquake failure of a retaining wall.
                   
Finally, for one of my recent abutment designs, the geotechnical report recommended the seismic earth pressure to be based on the coefficient equal to 50% of peak ground acceleration for non-restrained condition, and 75% of the PGA for restrained walls.  The resultant of that force was applied at the depth from the top of the retained soil equal to the difference between the toe and heel soil depths.   Did not make much difference.

Hope that helps,

--
Steve Gordin SE
Irvine CA



:
          I am hoping that some one who lives in shakey country can

          help. All of a sudden seismic design of residential basements
          walls has arisen here in not so shakey Ontario.  A fellow
          engineer called me as he had his sealing of drawings of a
          residence with 9 ft high basement walls questioned by a member
          of the BMEC (Ontario quasi government body, the Building
          Materials Evaluation Commission).  Beats me why such a person
          would even be involved because usually the local municipal
          building department only reviews such drawings.  The Ontario
          Building Code has a section on "housing and small buildings",
          i.e. under 600 sq m and 3 stories or less ( a presciptive
          section) which allows plain concrete basement walls up to 8 ft
          high. As soon as the wall is more than 8 ft high, it has to be
          approved by an engineer. Hence this problem arose.  He did
          call for reinforcing, but he wasvquestioned on seismic
          loading. I am hoping some of the helpful members can point me
          in the right direction to publications on this or give some
          advice.<br>
          Gary