Plaxis EA and EI from tutorial

[JSD1986]

Hi there

I am teaching myself plaxis 8 and have started going through the tutorials.

The first tutorial is 'settlement of a circular footing on sand'. The description is that it is a 2.0mtr dia footing.
When it comes to entering the material properties of the footing the tutorial guide says to use:
normal stiffness EA = 5x10^6 kN/m and:
flexural regidity EI = 8500.00 kN.m2/m

My question is how have they arrived at these A and I?

Heres how I would come to it.

A = (Pi).r^2 = (pi).1^2 = 3.14m2 (per single pile) >>>>> 3.14/2 = 1.57m2/m (mtr rate)
I = ((pi).r^4)/4 = ((pi).1^4)/4 = 0.785 m4 (per single pile) >>>>> 0.393m4/m (mtr rate)

Now working backwards to find E from EA >>> E = (5x10^6)/1.57 = ~3.2x10^6 kN/m2
and working backwards to find E from EI >>> E = 8500/0.393 = ~0.022x10^6 kN/m2


Now we know its a solid circular footing because they use it to find the pressure. The only thing I can think is that it has something to do with the model being axisymmetrical - when plaxis gives you the pressure for a described displacement the pressure it gives is for one radian.

I'm exicted about learning Plaxis and its very frustrating being stumped by something quite trivial.

Any help would be appreciated.

 

[mar2805]

Why would structural engineer need to learn PLAXIS geotehnical software?

 

[JSD1986]

You know that a foundation pile is both a structural and goetechnical element right?

 

[mar2805]

Realy ?! ;-)

 

[JSD1986]

so no one has any idea about the stiffness parameters?

 

[AndreBC]

@JSD1986 :
The example that you asked about is at Flexible Footing Section. Notice from the first paragraph,
"The calculation is now modified so that the footing is modelled as a flexible plate" (no longer circular).
For flexible plate, PLAXIS calculate A (area) from the plate as diameter x thickness.
And moment of inertia (I) will be I = 1/12 * diameter * thickness^3