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Plaxis EA and EI from tutorial

Plaxis EA and EI from tutorial

Plaxis EA and EI from tutorial

(OP)
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.

RE: Plaxis EA and EI from tutorial

Why would structural engineer need to learn PLAXIS geotehnical software?

RE: Plaxis EA and EI from tutorial

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

RE: Plaxis EA and EI from tutorial

Realy ?! winky smile

RE: Plaxis EA and EI from tutorial

(OP)
so no one has any idea about the stiffness parameters?

RE: Plaxis EA and EI from tutorial

@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


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