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# Re: Coefficient of Friction

• To: seaint(--nospam--at)seaint.org
• Subject: Re: Coefficient of Friction
• From: "Gerard Madden, SE" <gmse4603(--nospam--at)gmail.com>
• Date: Sat, 28 Aug 2010 23:34:32 -0700

Weather is cold again !  Had two hot days all summer, they were last week.

I deal with a lot on bad soil and often soils engineers give fairly low coef. of friction around here and when you put in vapor barries and the like it gets reduced more (by some). Or when you combine passive and friction, the friction values are reduced 50% further. So with the need for grade beams being pretty common, the passive usually takes care of it without resorting to anything overly tricky.

Pile foundation buildings as well, you gotta use the passive.

But I agree, in a lot of cases in decent soil, if you get a COF of 0.35 or so, you should be good to go.

-gm

On Sat, Aug 28, 2010 at 4:52 PM, V. Steve Gordin wrote:
Hi, Gerard,

How are you doing this Saturday afternoon?  How's weather in the Bay area?
It's such a nice and quiet family evening here in Vegas...

For shallow pads for heavy equipment, friction always does better.

But let's say we have a 10'x10'x4' footing for a 60K DL, 140K LL force.

The friction lateral resistance at mu=0.25 is [60K+60K (footing)]*.25=30K of resistance.

The passive resistance at a reasonable 250 pcf is 250*4'*4'/2*10'=20K...

Am I missing something?

V. Steve Gordin, Ph.D.
Structural & Civil Engineer
Irvine CA
949.552.5244

On Sat, Aug 28, 2010 at 4:10 PM, Gerard Madden, SE wrote:
Actually, passive pressure usually does more than friction in my experience to prevent sliding unless you have very shallow foundations. You can take care of most issues by utilizing grade beams to resist sliding.

2010/8/28 sgeconsulting

Richard,

This is true, but as we know, lateral bearing provides less resistance than friction - at least, for heavy equipment pads. Tricky...

SGE Mobile

On Aug 28, 2010, at 15:18, "Richard Hess" <RLHess(--nospam--at)HessEng.com> wrote:

That is why “footings” have to be buried into the soil where lateral forces are at least partially resisted by lateral resistance of the soil; not to mention the added weight of the concrete itself.

Richard Hess, S.E.

From: sgeconsulting [mailto:sgordin(--nospam--at)sgeconsulting.com]
Sent: Saturday, August 28, 2010 1:18 PM
To: <seaint(--nospam--at)seaint.org>
Subject: Re: Coefficient of Friction

The code implicitly disallows the use of friction to resist seismic forces, hence the use of "self-anchored" tanks does not appear a great idea. Besides, such tanks will be quite susceptible to wind when empty.

That said, we routinely use friction between the footings and the soil to resist seismic forces. How does that work from the code and just rational standpoints?

SGE Mobile

On Aug 28, 2010, at 8:29, "Richard Hess" <RLHess(--nospam--at)HessEng.com> wrote:

Paul,

That will not work if it is in earthquake country.  The vertical forces will dance it all over the place.

Richard Hess, S.E.

From: Paul Blomberg [mailto:paul.blomberg(--nospam--at)gmail.com]
Sent: Friday, August 27, 2010 12:49 PM
To: seaint
Subject: Coefficient of Friction

I have a client that wants their product tanks installed without anchorage (self-anchored) and I am trying to locate a coefficient of friction between the tanks (fiberglass and plastic tanks) and their base (concrete and gravel pads).  All these tanks are flat bottomed and supported on grade.

Does anyone have a reference with this information so I can check sliding?

Paul.