Soil / Earth Seismic Load on Structures on Slopes 2

[cpiedra23]

i remember there's some code line that says something to the effect of, where structures sit on sloping grades where the grade difference between the two opposing sides is 6' or over, the structure's LFRS shall be designed for seismic forces from the soil.

is this clause in the IBC somewhere? ASCE 7?

thanks in advance.

 

[wannabeSE]

There are plenty of rules of thumb and typical practices. But, there is no specific code language that I know. In chapter 11 of ASCE 7, the base is defined as "The level at which the horizontal seismic ground motions are considered to be imparted to the structure." I suggest reading the following resources:
ASCE 7-10's Expanded Seismic Commentary:

http://ascelibrary.org/doi/pdf/10.1061/9780784412916.chc11c22

Structure Magazine article Location of Base for Seismic Design

http://www.structuremag.org/wp-content/uploads/2014/08/C-StructPerformance-Kelly-Dec091.pdf

 

[sandman21]

IBC section 1803.5.12(1)

 

[cpiedra23]

@sandman21

thanks i've seen that clause... this is me being a code reader; it says the geotechnical report must have that information... but i don't see where the code says the building's LFRS must be designed for it?

i know it's implied, but i swear there was another section. maybe it was in an older code.

 

[wannabeSE]

The definition of base in the 1997 UBC is similar to ASCE 7 -10. I don't think it changes much. It requires some engineering judgment. If you think it should be more clearly defined, you might lobby the ASCE 7 code commitees to add another chapter

BASE is the level at which the earthquake motions are considered to be imparted to the structure or the level at which the structure as a dynamic vibrator is supported.

I think IBC §1803.5.12(1) doesn't directly relate to the location of the seismic base. It requires the soils report to include the seismic lateral loads on foundation walls and retaining walls with more than 6' of backfill. If a building has a full basement entirely below grade with stiff soils, the ground level may a suitable seismic base. The lateral loads from the soils report (along with the loads from the structure above) are used to design the basement. But, the ground motion is assumed to act on the structure at ground floor level.

 

[cpiedra23]

thanks for the input wannabeSE!

i wanna be an SE too (in california) - failed last october (both portions, sadly), but will be trying again this coming october. been going through SEAOC's 5 volumes, and soon will be looking at those bridge books by connor, and ppi's six minute solutions and their practice exam. i went through ppi's reference manual and hated the book (thought it was much to broad and vague).

good luck to you, whether awaiting april's results or for october's upcoming test!

 

[pinoycivilgeek]

Are those test for State Exams cpiedra23??