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# RE: Soil Pressure

• To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
• Subject: RE: Soil Pressure
• From: "Horning, Dick/CVO" <dhorning(--nospam--at)CH2M.com>
• Date: Wed, 27 Jan 1999 15:12:54 -0700

```OK, the math works using your assumption that the peak seismic soil pressure
would be 20H whether triangular or uniformly distributed - but according to
the soils reports I've seen the seismic pressures are much higher near the
ground surface, decreasing with depth, and it sounds as if this is what your
soils report is saying too, as I recall it.

BTW, if you're using UBC '94 and getting a seismic coefficient of .12 in
Zone 4, what are you using for Rw?  If I assume C defaults to 2.75 for a
stiff bldg, Rw backs out of the equation as 10 - can't think of any concrete
bldg system which goes this high.

-----Original Message-----
From:	Alex C. Nacionales [SMTP:anacio(--nospam--at)skyinet.net]
Sent:	Wednesday, January 27, 1999 1:55 PM
To:	seaint(--nospam--at)seaint.org
Subject:	RE: Soil Pressure

Dick,

Thank you for your correction of the terminology.

The geotechs may have a better explanation. What I have is just
a simple analysis in the absence of more complex methods.

The 20 pcf was taken original post regarding soil pressure.

I computed that if soil weight is 150 pcf
for a  sandy soil and if a use a g=.134( not .4 from my previous
post)
I get 150x.134 = 20pcf  as additional weight due seismic effects.

Seismic coefficients I  get for a four story RC building
in Zone 4 is about O.12

P = 20 pcf x 8' = 160 psf
for invert. triangle, solving Moment at wall base
M= 1/2x160x8x2/3= 426.6 plf
for rectangular,
M= 160x8x1/2= 640 plf > 426.6 plf

Alex C. Nacionales, C.E.
Iloilo City, Philippines

```