seismic design of retaining walls

[sginal]

I am currently working on a large scale project that involves over 40 new retaining walls. The project is located in an area that is Seismic Performance Category A. When I reference AASHTO (Division 1 - Section 5) regarding the need to consider seismic loading for these retaining walls it references me to AASHTO Division 1A - Section 6. Section 6 is Design Requirements for Bridges (& other highway structures) in Seismic Performance Category B. According to this section, bridges and other highway structures, retaining walls included, should be designed for the appropriate seismic loads. However, if I go to Division 1A - Section 5: Design Requirements for Bridges (& other highway structures) in Seismic Performance Category A, it states that there are no special design requirements for foundations and abutments of bridges in this category. It makes no direct reference to retaining walls in this category. Does this mean that regardless of a retaining wall's Seismic Performance Cateogry, it must be designed to resist seismic loads? What if the wall is in Seismic Design Category C, do you still reference Division 1A - Section 6 instead of Section 7? I am confident that seismic loads will not be the controlling load combination, but I do not want to have to show this for every single wall. Is there some way around this? Am I interpreting the code wrong? Any help would be greatly appreciated.

 

[Qshake]

Based on AASHTO, you would not have to design the wall for seismic loads if it is, in fact, in SPC A.

Perhaps the only points of consideration for the case of designing to SPC B is life safety and where does the wall's location fall with respect to the boundaries of SPC B.

In some cases, if a wall is not a life safety issue there will be no compelling reason to design to a higher category.

 

[sginal]

Qshake,

I agree that based on AASHTO (Division 1A - Section 5) that you do not have to design a retaining wall for seismic loads if it is located in SPC A--so long as the wall is not a life safety issue.

However, if you start in Division 1 - Section 5 of AASHTO (Retaining Walls), each subsection (5.5.4, 5.6.4, 5.7.4), except for an MSE wall, refers you to Division 1A - Section 6 (SPC B). The subsection for MSE walls allows the designer to ignore seismic loads unless the anticipated ground acceleration for the wall is greater than 0.29g (5.8.9). I guess my question is, why does AASHTO Division 1 - Section 5 refer you to Division 1A - Section 6 (SPC B) for all wall types (excluding MSE)? Why not reference the designer to the appropriate section of Division 1A based on the SPC of the wall?