Subgrade modulus of Reinforced concrete

[allimuthug]

HI ,

presently i am modelling the base plate and analyzing the behaviour of base plate under axial load and moment.
Can anyone let me know the subgrade modulus of reinforced conrete , which i have to use for finite element analysis

 

[BAretired]

Subgrade modulus is a term used to describe the properties of the subgrade. It is not used to describe reinforced concrete.

BA

 

[allimuthug]

I agree but i modeled the base plate as a plate element where the base is resting on the concrete, So what kind of support i would use can any one let me know.

 

[BAretired]

The modulus of elasticity of concrete is known approximately as a function of its strength.

BA

 

[JStephen]

That would be one of the drawbacks of using finite element analysis.

You could assume uniform loading under the base plate. Or linearly varying loading if there is a net moment.
For a small plate on larger concrete slab, you could assume that the mid-surface of the concrete was fixed, and treat the concrete above that as elastic in the vertical direction only.
You could include the concrete as part of the finite element problem also, which introduces other complications.
In a lot of cases, for the base plate design, assuming uniform loading on the bottom will be conservative.

Note that treating a subgrade as an elastic foundation (elastic vertically) can give considerably different results from treating it as an elastic solid. So it's an approach that is useful, but not necessarily an ideal solution, either.

If you have to use very crude approximations to get a solution to a problem, you should consider using very crude approximations that also simplify the problem. So perhaps uniform bearing and a yield-line analysis would be in order.

 

[KootK]

A while back, someone posted a video here that was an engineer from Utah summarizing a very well thought out FEM method that he used to assess anchor bolt and base plate stresses at braced connections. I remember there being information in the presentation to do with the concrete stiffness and I remember being surprised by it (not just concrete E). Hopefully someone will remember that presentation and post a link to it. I'd like to check it out again myself.

Like JStephen, for a real design I prefer a simplified non-FEM approach. Even the information in the video that I mentioned seemed a little questionable to me, despite it being very well thought out.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[BAretired]

If the column has axial load and moment, then the foundation will settle and rotate. If the foundation is a footing or pile, its rotation will be resisted by soil and that is where the subgrade modulus comes into play, not at the underside of base plate.

BA

 

[iv63]

KootK,
Is this presentation

https://www.aisc.org/UploadedContent/2008NASCCSessions/E1/default.htm

iv

 

[KootK]

That is the very presentation iv63. ThankS so much.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.