ASCE 7-16 Seismic Earth Pressure on Basement Walls

[TigerGuy]

How is everybody handling questions on Seismic pressures against basement walls? Typically, soil pressure against a basement wall is considered "at rest" loading. The only reference I've heard of on this topic is from 2010 Seismic Earth Pressures on Deep Building Basements by Lew, M., Sitar, N., Al-Atik, L., Pourzanjani, M. and Hudson, M.B.

Time has passed, and codes are updated. Now we are getting requests from structural engineers to quantify the lateral pressure on basement walls during a seismic event. From Lew, et al. 2010, we have the notion that basement walls are to be designed for the at rest conditions, with no increase for seismic loading, due to the lack of documented earthquake damage to basement walls.

Given the circular path ASCE 7-16 and IBC 2018 take us on, I would like some guidance on how to better understand this topic and be able to respond to client requests.

Thanks in advance

 

[HTURKAK]

I will suggest you to look CH .19 SOIL–STRUCTURE INTERACTION FOR SEISMIC DESIGN.

and the document at

https://www.nehrp.gov/pdf/nistgcr12-917-21.pdf

The Geotech people shall furnish the dynamic horizontal passive springs and vertical springs..

The dynamic soil loading, the passive resistance of the soil may cause additional loads on basement sidewalls.

 

[TigerGuy]

HTURKAK,

Thanks for the info. That document was published in September 2012. Is this the basis for the updates in IBC and ASCE 7? Or, are they going down a different path completely with their updates?

 

[ATSE]

Good question. Yes, in the last decade there has been a lot of published papers on seismic loading on walls of all types. And yet there is no broad industry-accepted code guidance.

"... due to the lack of documented earthquake damage to basement walls."
I know all these PhDs are real smart, but that was not a smart statement. Absence of evidence is not evidence of absence.
A 10ft tall basement wall in Southern California and a 10 tall basement wall in Texas should not both be designed ignoring seismic loads.

As a minimum, as a baseline I suggest seismic loads per AASHTO LRFD Bridge Design Spec (2017) suggests for walls and abutments greater than 8 ft tall.
I am not suggesting that AASHTO is the answer; some of that code language gives me heartburn. But it is a national committee-governed document that has relatively broad acceptance. And has incorporated some of the UCB / UCLA / Caltrans sponsored research.

Also note that Caltrans puts an upper limit cap on seismic lateral earth forces (amends AASHTO so it doesn't become ridiculous).

 

[epoxybot]

If you perform a google search for 'Nathaniel Wagner lateral earth pressure' you will get some more recent research data.
Nathanial Wagner of Slate Geotechnical Engineers, is a recent post-grad & recently licensed Geotech; who has been working on the Millennium Tower Perimeter Pile Upgrade.
What I don't understand (complete ignorance) is why the lateral earth pressure is applied to the basement/foundation wall area and not the shoring wall immediately abutting the basement/foundation wall.

 

[TigerGuy]

ATSE and epoxybot, great comments! I'll be studying Dr. Wagner's research in the coming weeks.

I guess I've not seen many basement walls with an additional shoring wall adjacent to them. I would think the lateral earth pressure should be applied to whatever structure in contact with the backfill, no matter what the arrangement.

 

[bones206]

In the past I've used Wood's elastic method for seismic earth pressures on non-yielding walls, such as concrete tanks or shafts. My reference for that method is ASCE 4-98. Might be outdated now...

 

[ATSE]

Wood and Ostadan have gone the way of the dodo bird.
Attached is an easy to read Wagner paper.