FEA Plate stress

[DaveHolder]

I have run Concrete element as FEA on Strand7, the C40/50 concrete is surrounding Slot made of Iron, and the load 900 kN . My question is how to check the results of plate stress whether are they correct or not ? The maximum results for Plate stress are XX 135 mpa, yy 115 mpa and xy 48 mpa.

Many Thanks
Leo

 

[KootK]

You could:

1) Find an approximate had calculation to verify your numbers. Perhaps something from Roark's stress and strain formula book.

2) Compare output with another software package that you know well.

3) Refine your meshing in intervals to gauge sensitivity to element size.

4) Check overall equilibrium of the applied loads with the computed reaction.

5) Ensure that the displacements and stresses are consistent with your intuition.

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.

 

[DaveHolder]

The maximum node Displacement is 0.121m and node reaction is 237 kN. The Plate forces are quite similar to the stresses outputs. What is the value which maximum stress should not exceed?

Thanks

 

[KootK]

In the context of an RC plate design, you will usually work out design moments and shears and then provide reinforcement to suit those moments and shears. As such, there often isn't really a target stress range as you might have when designing with steel.

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.

 

[DaveHolder]

If you don't mind have you got any worked example

Many thanks

 

[KootK]

You might try:

1) general purpose concrete design texts that cover two-way slab design.
2) verification manuals for SAFE or whatever software you're using.

I don't have a canned example to share I'm afraid.

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.

 

[DaveHolder]

I am not sure if there is formula where I could use the modulus of elasticity of concrete to determine the allowable stresses? Please help me to refresh my memory

 

[KootK]

I am not sure if there is formula where I could use the modulus of elasticity of concrete to determine the allowable stresses? Please help me to refresh my memory

Not unless you're attempting to design plain, un-reinforced concrete which would be unusual. There aren't really "allowable stresses" in the traditional sense in modern reinforced concrete design. You simply proportion your cross section and specify your reinforcing to supply the required, ultimate flexural capacity.

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.

 

[IDS]

Assuming you are running a licensed copy of Strand7 you should have a look through their web-notes for information on modelling reinforced concrete, and what to do with the results.

It sounds like you are not familiar with reinforced concrete design, so I would suggest refreshing the basics of that before going too far with the analysis. As noted by KootK, you will need to extract bending moments and shear forces (and axial forces if the loads are in-plane), and calculate the concrete compression and steel tension from that.

But that said, if you have modelled the element correctly the maximum compressive fibre stress from the model will be of the same order as the maximum compressive stress in the concrete, so if you are getting 135 MPa, that is way too high for concrete with a compressive strength of 40 MPa.

If you would like to upload your .st7 file I would be happy to have a quick look at it.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[Brad805]

If you want to read about methods to design concrete from a basic linear finite element analysis you could read the attached. Mohr circles and the likes. Great fun...

 

[DaveHolder]

The model is not RC, I realized what was the cause of large stresses which is due to inaccurate loads values. The maximum stress output I got is 14.6 MPa.

My question is if the maximum stress is less than the Compressive strength which is 40 MPa, then the results are reliable?

Many thanks

 

[Trenno]

Results don't necessarily need to be less than f'c to be reliable or accurate. Garbage in, garbage out.

But if the strain is less 0.003, concrete crushing shouldn't be an issue.

 

[DaveHolder]

The maximum stress was 14,6 MPa, and Young's modulus is 35000 MPa, therefore the strain is 14.6 over 35000 = 0.0004 which is less than 0.003. I love the expression of Garbage in Garbage out, I hope that is not what you do.

Many Thanks