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# Re: CSA A23.3 PG 9-16

• To: <seaint(--nospam--at)seaint.org>
• Subject: Re: CSA A23.3 PG 9-16
• Date: Mon, 19 Aug 2002 12:13:22 +0200

```----- Original Message -----
From: Zhang, Michael <michael.zhang(--nospam--at)shawgrp.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Tuesday, May 28, 2002 10:59 PM
Subject: RE: CSA A23.3 PG 9-16

Daryl,

Thank you very much for your explanation. Now I know much more of the Design
Example.

Regards,

Michael

-----Original Message-----
From: Daryl Richardson [mailto:h.d.richardson(--nospam--at)shaw.ca]
Sent: Tuesday, May 28, 2002 4:31 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: CSA A23.3 PG 9-16

Michael,

Thank you for the clarification yesterday.  Sorry I couldn't get back
to you yesterday but something else came up.

I am not familiar with the derivation of the subject equation; but if
you accept the values for r1 and r2 (which actually come from step 6)
then, using reverse engineering, perhaps I can make the following
clarifying statements.

1.)  The equation seems to be dealing with a phenomenon similar to
punching shear in slabs and this is an attempt to assess what part of
the pile loading is outside of the critical d/2 distance from the
support.

2.)  The first term in the equation, r1(2Qpr) deals with the two side
piles.  Qpr is the individual pile load; 2 is the number of side piles;
and r1 is the fraction of the pile loading which is beyond the critical
d/2 from the side face of the column (support) and would, hence,
contribute to the shear force.

3.)  The second term in the equation, (1-(1-r1)(1-r2))(4Qpr) deals with
the four corner piles.  Again, Qpr is the individual pile load; 4 is the
number of corner piles; r1 is the fraction of pile loading beyond the
critical d/2 from the side face of the support; and r2 is the fraction
of the pile loading which is beyond the critical d/2 from the end face
of the column (support) and would, hence, contribute to the shear force.

4.)  The ingenious part of the equation is the part (1-(1-r1)(1-r2).
Note that if either or both r1 and r2 are 0 (all of the pile loading is
closer than d/2 from the "support" and should not get included in the
analysis this term becomes 0; if both r1 and r2 are 1 (all of the pile
loading is further than d/2 from either face of the support and should
get included in the analysis this term becomes 1.0; if r1 and/or r2 are
fractional then this term is a positive fraction and a fraction of the

This equation seems to me to be completely valid academically
speaking.  Practically speaking I do have some doubts.  I have no
comment on the validity of the values for r1 and r2; you didn't ask and
I didn't review the matter.  On the practical side, I have yet to see a
piling job that didn't have some piles out of position by 4 or 6
inches.  As a question, what should you do when you have non uniform
pile spacing or unequal loading (say from an applied moment); should you
not design for the most critical pile?  My personal philosophy in these
matters is: don't design these things too close to the limit; if
something can go wrong it probably will; foundations (and columns, for
that matter) are a very cheap place to over design and a very expensive
place to have problems.

Anyway, Michael, I hope my ramblings have been helpful to you.

Regards, and sorry I took an extra day,

H. Daryl Richardson

> Zhang, Michael wrote:
>
> For Engineers familiar with Canadian code:
>
> In Step 7 in page 9-16 of CSA A23.3-94, there is a formula Vf =
> r1(2Qpr)+(1-(1-r1)(1-r2))(4Qpr), I failed to get it from basic
> mathematical method, could anybody inform me of its background?
>
>
>
> Regards,
>
>
> Michael
>
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