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# Re: UBC CODE INTERPRETATION

• To: <seaint(--nospam--at)seaint.org>
• Subject: Re: UBC CODE INTERPRETATION
• From: "Dan Goodrich" <dang(--nospam--at)karren.com>
• Date: Wed, 6 Dec 2000 13:31:29 -0700

```I had assumed that the loads given were at the allowable level.  The
reasoning for using a smaller value than the full passive pressure is that
it normally takes a significant amount of movement to "mobilize" the
pressure.  I also make the assumption that the compaction outside the
building will probably not be very good.  In other words, passive
pressure can help, but be careful.

Dan Goodrich, P.E.

> Remember that capacities and demands need to be compared on like bases.
To
> use factored loads (demands) and compare to allowable passive pressures
> (capacities), friction etc. is not comparing "apples to apples."  Few
> geotechs I've worked with have made the leap to providing values
> corresponding to factored loads yet as their standard practice.  When you
> discuss it with them they typically scratch their heads and tell me,
"Well,
> I have used such and such factor of safety to obtain the allowable values,
> you figure out how you want to convert to factored loads."  As a result, I
> typically convert the factored loads back to allowable loads and make the
> comparison on allowable stress basis.
> Regards,
> Bill Cain S.E.
> Oakland CA
>
>
>
>
> -----Original Message-----
> From: Dan Goodrich [SMTP:dang(--nospam--at)karren.com]
> Sent: Wednesday, December 06, 2000 8:44 AM
> To: seaint(--nospam--at)seaint.org
> Subject: Re: UBC CODE INTERPRETATION
>
> > You should include seismic acceleration on the foundation when
> checking
> > sliding of the overall structure (i.e., sliding force = 7.25 kip
> per your
> > example). The earthquake motions are imparted to the structure at
> the
> bottom
> > of the foundation (via friction). The inertia of the foundation
> will try
> to
> > resist lateral movement, i.e. it doesn't know how to interpret the
> code,
> it
> > just reacts to acceleration (F=Ma).
> >
>
> It would also seem to be appropriate to include passive pressure of
> the soil
> against the foundation to help against sliding.  I would not use the
> full
> passive
> pressure value though.  Apply an appropriate factor of safety based
> on your
> knowledge of the soils.  Your geotech could help.  Also, you should
> call for
> compaction of the soil around the outside of the foundation if you
> intend to
> use passive pressure.  If sliding is that much of a problem, bury it
> down
> deeper into the ground.
>
> Dan Goodrich, P.E.
>
>
> > > -----Original Message-----
> > > From: Vinod Sahni [mailto:SAHNIVK(--nospam--at)nv.doe.gov]
> > > Sent: Wednesday, December 06, 2000 9:29 AM
> > > To: JLUTZ(--nospam--at)earthtech.com; seaint(--nospam--at)seaint.org
> > > Subject: Ref: UBC CODE INTERPRETATION
> > >
> > >
> > > But I probably got misunderstood or I did not clarify my
> > > question enough.
> > >
> > > Basically, the question is this:
> > >
> > > Let us assume the following -
> > >
> > > Equipment Wt = 5 kip,  Accel at CG of Equipment = 0.65g
> > > Foundation Wt = 10 kips, Max Ground Accel = 0.40g
> > >
> > > Let us calculate base shear for foundation sliding check:
> > >
> > > Sliding Force = 5 kip x 0.65 = 3.25 kip ( I believe this will
> > > meet code).
> > >
> > > OR,
> > >
> > > Force = 5 kip x 0.65  +  10 kip x 0.40  =  7.25 kip (I do not
> > > think code
> > > requires this method).
> > >
> > > I would appreciate your looking into this further and giving
> > >
> > > Thanks again.
> > >
> > >
> >
> >
>
>
>
>

```