Seismic loads on retaining & basement walls using IBC

[emceditor]

The International Building Code (IBC) requires a seismic loading on all retaining walls. A common method of calculating the lateral soil pressure created by seismic activity against “yielding walls”, is the Mononobe-Okabe Method, and the Wood (1973) method, as presented in "Geotechnical Earthquake Engineering" by Steven L. Kramer, for the non-yielding walls. Within this method, there is a coefficient “kh” that modifies the force generated by the weight of the soil failure wedge behind the wall. "kh" is equivalent to the design spectral response acceleration, which ranges from the 0.2 sec period (SDS) to the 1.0 sec period (SD1). The value of “kh” makes a huge difference in the magnitude of the lateral force on the wall. Does anyone know if previous Seismic codes addressed whether to use the SDS or SD1 factor?

 

[haynewp]

I've been trying to figure out the same thing, and the only thing I have found is that many people have ignored seismic loads on retaining walls for many years. I certainly don't agree.

 

[whyun]

IBC is not adopted in my area currently; however, I believe there is a code provision which states that a seismic force due to soil be considered if the basement wall is retaining more than 12 feet. this implied that seismic force due to soil may be ignored for retained soil less than 12 feet. i do not know the reasons why.

typically, the seismic force due to retained soil are available in a geotechnical report for a given site.