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RE: Sliding - Friction & passive resistance

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Unlike footnote 2, Table 18-I-A does not say 1/3 increase in tabulated lateral bearing capacity is allowed for short-term loads. However, considering footnote 3 which allows us the values to increase to 2 times as much for *poles* as long as increased displacement at top is not a problem, this is a displacement issue rather than strength issue. Geotech reports also give different lateral capacities for different displacements (non-linear p-y curve).  Higher capacity employed means higher foundation flexibility.

 

 "Haan Scott M DPW CIVIL ENGR(n)" <scott.haan(--nospam--at)richardson.army.mil> wrote:

Learn something new every day. Thanks.  Now I have a code question on this table.  Can you increase the lateral bearing values by 1.33 for short term loads?  Can you do this for the non-constrained formula in 1806.8.2.1? Why - why not?  The last paragraph in 1805 appears to infer that you can.
-----Original Message-----
From: C Chan [mailto:seaint_list(--nospam--at)yahoo.com]
Sent: Thursday, November 14, 2002 2:14 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Sliding - Friction & passive resistance

Table 18-I-A, footnote 4 says "Lateral bearing and lateral sliding ***resistance*** may be combined". Resistance capacity is given for type 5, clay only, which is due to adhesion - 130psf*contact area. I do not think this is irrational.

 "Haan Scott M DPW CIVIL ENGR(n)" <scott.haan(--nospam--at)richardson.army.mil> wrote:

I believe I will use this advice.  However; see 97 UBC Table 18-I-A footnote 4, which reads "lateral bearing and lateral sliding resistance may be combined."  Noone ever said the code was rational.

 -----Original Message-----
From: C Chan [mailto:seaint_list(--nospam--at)yahoo.com]
Sent: Thursday, November 14, 2002 8:10 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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