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RE: Concrete Spring Constant for Base Plate Modeling

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John,
I would suggest the procedure in Omer Blodgett's "Design of Welded Structures".  It accounts for the stretch in the anchor rods and the strain in the concrete.  As with all of his work, it is very logically presented and well thought. 
 
It is easily presented in a MathCAD template. 

Regards, Harold Sprague






Date: Fri, 30 Jan 2009 11:22:07 -0800
Subject: Re: Concrete Spring Constant for Base Plate Modeling
From: jeongidea(--nospam--at)gmail.com
To: seaint(--nospam--at)seaint.org

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 <dfisher(--nospam--at)fpse.com> 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
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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

 



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