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# RE: Concrete Spring Constant for Base Plate Modeling (correction)

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: Concrete Spring Constant for Base Plate Modeling (correction)
• From: "Wesley Werner" <wwerner(--nospam--at)conewago.com>
• Date: Fri, 30 Jan 2009 15:08:00 -0500

Make that 6,000 psi grout.

Wesley C. Werner

From: Wesley Werner [mailto:wwerner(--nospam--at)conewago.com]
Sent: Friday, January 30, 2009 2:55 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Concrete Spring Constant for Base Plate Modeling

John,

Try this link http://www.aisc.org/UploadedContent/2008NASCCSessions/E1/default.htm . A few slides into the presentation the presenter talks about spring constants. He concludes that for 3,000 psi concrete the value is about 1,000,000 lb/in. For 3,000 psi grout the value would be 2,000,000 psi.

Wesley C. Werner

From: john yang [mailto:jeongidea(--nospam--at)gmail.com]
Sent: Friday, January 30, 2009 2:22 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Concrete Spring Constant for Base Plate Modeling

Hmm,  just pick the number. However, the question is what is the reasonable number.

Depending on spring constant,  it will change tensions on the anchor bolts.  If somebody starts with no idea of bolts' tensions,  they may come up with very small number if they use very flexible springs.

Anyway,  the reason that I am modeling the base plate instead of using  AISC design guide is my base plate has re-entrant corner inside and have both direction lateral loads (of course both direction shears and moments) at the same time.

I want to know how much stress concentrations at the re-entrant corners are and I don't think AISC design guide covers this situation.

Thank you so much.

John

On Fri, Jan 30, 2009 at 10:42 AM, David Fisher wrote:

Hooke's Law is bascially F = k*x

F, I assume you know.

x = say 0.1" just to pick a value, solve for "K" which is your spring constant.

Not sure what your structure/foundation type is or load magnitudes…

That's a good place to start, if the results don't make sense, then reduce the value of "x" as necessary

To make the results reasonable.

The bigger question might be, why are you modelling this condition this way?

AISC has spent years developing the base plate design criteria.

Can't you just use that design procedure?

From: john yang [mailto:jeongidea(--nospam--at)gmail.com]
Sent: Friday, January 30, 2009 12:38 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Concrete Spring Constant for Base Plate Modeling

How can I assume "the extension"?  For spring, k=EA/L I know E and I know A and I know concrete compressive strain (0.003).  The problem is L or deltaL.  How can I assume those?  Will L be full length or depth of member? How much will I assume delta L for it?

Thank you so much.

John

On Fri, Jan 30, 2009 at 9:31 AM, David Fisher <dfisher(--nospam--at)fpse.com> wrote:

Try my favorite formula, the foundation for structural engineering:

Hooke's Law:

"as the extension, so the force…"

David L. Fisher SE PE

Fisher and Partners - Cayman

372 West Ontario Chicago 60610

75 Fort Street Georgetown Grand Cayman BWI

319 A Street Boston 02210

312.573.1701

312.573.1726 facsimile

312.622.0409 mobile

www.fpse.com

From: john yang [mailto:jeongidea(--nospam--at)gmail.com]
Sent: Friday, January 30, 2009 11:29 AM
To: seaint(--nospam--at)seaint.org
Subject: Concrete Spring Constant for Base Plate Modeling

Hi,
I am modeling base plate on the 6000 psi concrete column and I want to put concrete compression only spring to represent concrete.  The problem is what is the compressive spring constant of concrete.  Could you help me to get it?

Thank you so much.

John