Flat plate analysis

[HoshangMustafa]

Hi

I tried modeling Example 13.3 from Nilson's Design of Concrete Structures SI unit 14th edition textbook. Please find the attached link:

Panel cut A-A1 displays MYY Automatic direction Integral value of -87.93(kN*m/m)*m for ULS case component 5

Table 13.8 of the textbook displays 113kN*m.

Panel cut A-A4 displays MYY Automatic direction Integral value of -84.44(kN*m/m)*m for ULS case component 5

Table 13.8 of the textbook displays 75kN*m.

Panel cut A-A2 displays MYY Automatic direction Integral value of 274.94(kN*m/m)*m for ULS case component 4

Table 13.8 of the textbook displays 271kN*m.

Panel cut A-A3 displays MYY Automatic direction Integral value of 88.52(kN*m/m)*m for ULS case component 4

Table 13.8 of the textbook displays 90kN*m.

Panel cut A-A2 and A-A3 results seem comparable whereas results for panel cuts A-A1 and A-A4 don't seem comparable.

Any thoughts would be highly appreciated.

[HoshangMustafa]

Hi @DonBAE 

What if I had a 3D frame with slabs, beams, and columns. How one can get column axial forces? 

I meant 

What if I had a 3D frame with slabs, and columns. How one can get column axial forces? 

[DonBAE]

from the column bar elements, that is why you model them.

[HoshangMustafa]

Hi @DonBAE 

Is there any workaround to get column axial forces from slab results?

[DonBAE]

I don’t understand why you won’t just get the column force from the actual column it is the most accurate place to retrieve that information.

is it possible to compute the column reaction from plate section results, not really you could approximate the reaction by taking several section cuts and computing the difference and averages but it makes zero sense to go through that effort when you could simple get the correct result in two seconds looking at the column bar forces.

[DonBAE]

I suggest you study the free textbook available from here:

https://www.mastan2.com/textbook.html

and the perhaps also find a copy of this text:

https://www.amazon.com/Finite-Element-Design-Concrete-Structures-2nd/dp/0727741896

[DonBAE]

These two would be other books to review:

A First Course in the Finite Element Method by Logan

Concepts and Applications of the Finite Element Method by Cook

[HoshangMustafa]

Hi @DonBAE 

I calculated column axial load manually for Example 13.3.

Please find the attached picture.

Manually: 375

Robot: 335.71

If this is correct, then these results are comparable.

[DonBAE]

I am not able to follow your calculation. 

Remember the equivalent frame analysis is a 2d analysis of a single strip of the slab in one axis and robot is a full 3d analysis. Traditionally axial load was determined on a tributary area basis because the strips in each direction would include overlapping load areas.

refer to design examples by SPSlab:

https://structurepoint.org/publication/design-examples.asp

[HoshangMustafa]

Hi @DonBAE 

My mistake. Please find the attached link:

I think it's comparable with Robot results.

[DonBAE]

From your hand calculation reaction should be the difference in bay shear so 713 Kn. By trib area axial force should be around 673 Kn.

looking at your model again your support condition for the columns up is incorrect the support condition for the top nodes should allow for vertical movement.

[HoshangMustafa]

Hi @DonBAE 

Thanks Celt83

You wrote:

refer to design examples by SPSlab:

https://structurepoint.org/publication/design-examples.asp

Applying these in Example 13.3 the results will be as:

Try it. It corresponds to Robot column axial load.