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Modeling mats with solids

Modeling mats with solids

Modeling mats with solids

(OP)
I have a reinforced concrete mat that is 3 feet thick. I have typically used plate elements to model this in the past. But some engineers think that when a mat gets to 3-5 feet in thickness; it is better to use solid elements.

I'm not so sure. It's been my experience that they [i.e. 8 noded solid elements] tend to overestimate stiffness (through the shear locking phenomenon) and thus would attempt to transfer more load through shear rather than through bending. Thus, the results would be highly questionable (i.e. the stresses). What are your thoughts on this?
 

RE: Modeling mats with solids

Seems like I've seen this question before, but I can't seem to find it in recent history.  Can you give a little more information on the geometry other than 3 feet thick?  (For instance, how big is the area represented by this mat, what type of concrete, etc.)

RE: Modeling mats with solids

(OP)
The mat is 26' x 13' sitting (concentrically) on 6 caissons (that are 5' in diameter). The concrete is 5000 psi.

But really I'm curios as to people's thoughts on this in general. I've heard the argument [before] about using solids to represent thick mats. I've just never bought it before because of the lousy results I've gotten with using solids.

RE: Modeling mats with solids

I'm not very knowledgable about concrete...I just figured others would need the basic geometry to really respond.  My general thought is that you should be using bricks, but the material model that you choose is probably much more important than the geometry.  I assume you are performing static analyses, but are you running linear or non-linear?  And if non-linear, what material model?  I know there are a couple of good models out there for concrete...

RE: Modeling mats with solids

(OP)
Static, linear analysis.

RE: Modeling mats with solids

3doors:

It really depends on how good your specific model is and whether you have enough elements through the thickness (as well as over the area) to pick up the actual situation....

Basically a poor model will give poor results and a good model will give good results....Since you will have both bending and shear present in the slab portions and at the cassions you will require several elements through the thickness to represent the actual situation...

In general solids will give good results if used properly.

Ed.R.

RE: Modeling mats with solids

(OP)
Thanks for the points EdR.

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