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Re: Definition of Pier in ACI 530-02

• To: seaint(--nospam--at)seaint.org
• Subject: Re: Definition of Pier in ACI 530-02
• From: "Gerard Madden, SE" <gmse4603(--nospam--at)gmail.com>
• Date: Thu, 3 Aug 2006 16:12:01 -0700

Pilasters are not normally designed to resist in-plane lateral loads like a Wall Pier or Shearwall. If so, then design it as a frame column.

Doing a relative rigidity analysis will let you know how much force the segment is sucking into it, that's why it's a good thing to have a few shearwalls to suck all the load, or have a number of wall piers that take a relatively equal portion of the load to make it manageable. If you have a column in a series of panel or wall openings, it will generally receive very little lateral load unless the wall line is very open and there are few stretches of solid wall.

The wall pier has special detailing requirements for confinement/ductility, that's why they have the separate definition.

-gm

On 8/3/06, Joe Grill <jgrill(--nospam--at)swiaz.com> wrote:

I thought pilasters were for elements within a wall.

Joseph R. Grill, P.E. (Structural)

Shephard - Wesnitzer, Inc.

Civil Engineering and Surveying

-----Original Message-----
Sent: Thursday, August 03, 2006 2:16 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Definition of Pier in ACI 530-02

Piers are generally for thin elements like walls of concrete or cmu. THis is more of a column with the dimensions in both directions being fairly close. See UBC/CBC section 1921 for the wording they use. The oddball part of your thing is the length is only 30" high, therefore its a pedestal. If it were taller, then it would just be a column.

If it's less than 3x it's thickness, it's a column
If it's greater than 6x it's thickness, it's a shearwall
If it's height is greater than 5x it's length, then its a column again.

Think of a 4 foot stretch of a wall that's 6-8" thick, that's a pier or "Wall Pier" in this case

-gm

On 8/3/06, Joe Grill < jgrill(--nospam--at)swiaz.com> wrote:

I can't quite get my pea brain around the definition of a pier in the ACI 530-02 document.  It states:

"An isolated vertical member whose horizontal dimension measured at right angles to its thickness is not less than 3 times its thickness nor greater than 6 times its thickness and whose height is less than 5 times its length."

I have a "pier" that is 24"x28"x 30" high.

I see the thickness=24", L=28", h=30"

3 x thickness = 72"

6 x thickness = 144"

5 x L = 140"

The horizontal dimension measured at right angles to its thickness = 28" which is less than 72" therefore the way I read this this is not a pier.

What am I not getting here?  I see a "pier" as being the same as a "pedestal" in ACI 318-02, but the definition of a pedestal is clear.

Thanks,

Joe

Joseph R. Grill, P.E. (Structural)

Shephard - Wesnitzer, Inc.

Civil Engineering and Surveying

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-gm

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-gm