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# RE: Soil Pressure

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: Soil Pressure
• From: "Alex C. Nacionales" <anacio(--nospam--at)skyinet.net>
• Date: Thu, 28 Jan 1999 14:08:41 +0800

```Dick,

I used Rw = 10(Concrete Special Moment Resisting Space Frame) taken from our
1992 National Structural Code. The seismic forces  in our code conforms with
1988 SEAOC. I recall that this is 12 in UBC 88. I do not think its a
misprint
maybe our code writers made some minor changes to be safer.

C =2.75 (max. value), can be used for any structure regardless of soil type
or structure period.

Base shear formula, V = ZI(C/Rw)W = .40x1x(2.75/10)W=.11W (to be exact)

May I ask what is the Rw value in UBC 1994? Maybe the formula is different.

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

> -----Original Message-----
> From: Horning, Dick/CVO [mailto:dhorning(--nospam--at)CH2M.com]
> Sent: Thursday, January 28, 1999 6:13 AM
> To: 'seaint(--nospam--at)seaint.org'
> Subject: RE: Soil Pressure
>
>
> 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.
>

```