# How to determine the Foundation Stiffness of a beam

FedeZappa
Member

Hello everybody.

how can I relate the Foundation Stiffness offered by a circular section beam with its elastic modulus?

The only thing that I came up with is the following:

I set the elastic support on an area equal to the cross section area of the beam, and then I set the Foundation Stiffness dividing the elastic modulus for the length of the beam.

The resulting units are correct, and I believe also the physics are correct, but I really would like a confirmation of that.

Thank you very much,

Federico

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## Answers

@FedeZappa

I found a pdf file while searching on Foundation Stiffness.

Are you asking about Foundation Stiffness for a pile in soil?

Hi Peter,

I tried to be as general as possible, but probably that was not the best idea.

Basically, I'm trying to model a plate that divide 2 volumes. The two volumes pressure is different, and the differential pressure deform the plate.

The focus of my study is the deformation of this plate.

Since I want to reduce the deformation of the plate, I thought about using a screw that "try to keep in place" the plate mitigating the deformation.

I'm not interested in the screw, I'm interested in the effect that this screw have on the plate deformation, so, I thought about modeling it with an elastic support.

The problem is that I'm not sure about how to set the elastic foundation stiffness support.

In the image attached you can see a schematic and a summary of what I wrote up here.

Thank you for your patience,

Federico

@FedeZappa

The stiffness of a bolt is AE/L where A is the cross-sectional area, E is the Young's Modulus and L is the length of the bolt.

@peteroznewman

I agree with you, however, the model asks me to input an EFS value. that is in [F/L^3]. The stiffness unit is [F/L].

Should I just divide the stiffness for the area of the bolt? So, Basically the EFS will be equal to E/L, where E is the Young's Modulus and L the length of the bolt.

This, value, applied to an area equal to the screw cross section will result in a stiffness that it's exactly the same of the stiffness provided by the bolt.

Am I right?

Thank you very much,

Federico

@FedeZappa It sounds right to me.