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RE: Sliding - Friction & passive resistance

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Title: RE: Sliding - Friction & passive resistance

I think the intent of 97 UBC Table 18-I-A footnote 4 is that you can use lateral bearing with either friction or cohesion because the footnote number is referenced for "lateral sliding" not just "resistance".  Likewise for the 2000 IBC 1804.3.  Example 29 part 3 of the my "2000 IBC  Structural/Seismic Design Manual - Volume 1 Code Application Examples" shows friction combined with lateral bearing.

-----Original Message-----
From: Sherman, William [mailto:ShermanWC(--nospam--at)cdm.com]
Sent: Friday, November 15, 2002 5:40 AM
To: 'seaint(--nospam--at)seaint.org'
Subject: RE: Sliding - Friction & passive resistance


NAVFAC 7.02, Figure 15 on page 83, suggests a sliding factor of safety of
1.5 when passive pressure is not included with friction/cohesion and 2.0
when passive pressure is included.

My own approach is to use a conservative passive pressure combined with
friction, based on wall deflection but not translation. I generally either
use at-rest pressure or one-half ultimate passive pressure for my resisting
soil pressure when combined with friction for sliding resistance. (This is
based on EM 1110-2-2502, Corps of Engineers publication or ASCE's "Retaining
and Flood Walls".)
 
Friction on side walls could be estimated by calculating the lateral soil
force on the side walls and multiplying by the soil friction coefficient.
But a question would be whether the pressures and friction coefficient on
the side walls are affected by seismic effects?


William C. Sherman, PE
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)cdm.com

-----Original Message-----
From: C Chan [mailto:seaint_list(--nospam--at)yahoo.com]
Sent: Thursday, November 14, 2002 10:10 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: Sliding - Friction & passive resistance

Static frictional resistance occurs only when the wall is stationary. When
the wall is stationary, there is no passive pressure being mobilized. After
sliding starts, kinetic frictional resistance comes into play, which is
always less than its static counterpart. I believe, the usual factor of 0.25
or 0.3 prescribed by the Geotech is the coefficient of static friction. So,
is it rational to combine frictional resistance (i.e. W x static friction
coefficient - assuming granular soil, not cohesive soil) and passive
resistance together to resist seismic forces for a critical element like
shear wall?
What do you think?

 RDAHLMANN(--nospam--at)aol.com wrote:
I have a question about sliding in long shear walls. In high seismic
regions, sliding can govern footing sizes. Resistance is provided by the
friction factor times the dead load weight (times appropriate factors) plus
any passive pressure. This can also include return walls.

For long shear walls, it seems like there should be some sort of side
friction factor also (similar to caisson skin friction). I have not seen
this anywhere, but I would like some input about this possibility.

Thanks
Richard Dahlmann, P.E.
Phoenix

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