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RE: UBC CODE INTERPRETATION (ZONE 4)

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For the equipment pad you describe I usually compute it two ways. At the top
of the foundation for holddown bolt calculations, and at the base of the
slab for overturning. I would ignore soil loads on the slab at the edges. 

-----Original Message-----
From: Vinod Sahni [mailto:SAHNIVK(--nospam--at)nv.doe.gov]
Sent: Tuesday, December 05, 2000 7:12 AM
To: seaint(--nospam--at)seaint.org
Subject: UBC CODE INTERPRETATION (ZONE 4)


Hi,

I have a couple of questions (probably too simple for most of you even to
consider on this list).  I would appreciate in advance for your opinion.
I have an argument going over the following.

To simplify the problem, it is an equipment item sitting on a ground
supported slab (18" thick, top of slab 6" above grade).

1.  Do you apply horizontal seismic acceleration to the weight of the slab
or foundation?  I have never seen this done  before.  From the definition of
"BASE" UBC Section 1627, to me it is obvious that you do not consider
foundation for two reasons (base level and dynamic vibrator).

2.  What minimum safety factor is required against seismic overturning? 
My reading is, SF against wind is 1.5.  For seismic resistance 1.0 is
acceptable.  Obviously for a tall slender structure/equipment I may choose
to raise that to 1.5.  Consider it to be a static loading scenario.  For
sliding,
SF is always 1.5 minimum.

Please let me know your interpretation of UBC 97 and how do you handle
it.

Thanks a lot!

Vinod Sahni, SE