Seismic design of MSE structures

[msucog]

Related to seismic design in MSE structures, which return period should the designers be using to determine the design acceleration? Also shouldn't the soil's amplification at each wall's specific location be used in the design when determining the appropriate acceleration to use in their design (i.e. seismic site class)?
Any explanation or insight would be greatly appreciated.

 

[VoyageofDiscovery]

Hi msucog,

To answer your first question, this depends on what your MSE structure supports. For example rail, consult the AREMA Code, highways consult AASHTO, buildings consult the loacl building code.

VOD

 

[msucog]

in your opinion, is there any reason why commercial construction should be able to follow the older AASHTO code if the project has nothing to do with highway projects?

I happen to have researched my question prior to asking it. In a sense, i am looking for some reasonable argument to refute my own opinion. I am not familiar with AREMA, but I am only interested in MSE walls related to commercial construction. As you are probably aware, the design return period for AASHTO is much less conservative than the return period by IBC (primarily because the public cannot afford to upgrade all current bridges to meet the higher return period). In commercial work, I've seen designers using the older AASHTO recommendations (10% in 50 yrs- ~500 ry return period) which also happens to be in line with the out-dated NCMA recommendations instead of following the IBC requirements (2% in 50 yrs- ~2,500 yr return period). The designers also happened to use the accerlation at the bedrock level and did not use a soil amplification factor. Under the logic of trying to use the less conservative period, I would think that they should at least use the current LRFD period of 5% in 50 yrs - ~1,000 return peiod.

I personally think that commercial work should fall under IBC and NEHRP requirements. NEHRP is very clear as to the requirements for MSE walls. NEHRP essentially says that MSE walls must be designed to resist seismic forces in the same way buildings are designed which is to use the ~2,500 year return period along with the soil site factor determined by the seismic site class at each wall location.

If someone has other references they can present to argue the reason for not following the current code or to point out confusion on my part, please post.

 

[VoyageofDiscovery]

The 2500 yr return period is newer and if IBC requires this and this supercedes the local building code, then this new requirement must be followed.

Using old AASHTO may have been acceptable in the past as the return periods may have been similar, however newer AASHTO requirements will eventually be updated.

VOD