# AQUA Report - Design forces and moments

Hi,

as I am quite unexperienced with Sofistik - especially with composite structures - I tried to comprehend how Sofistik calculates the plastic design values shown in the table below.
The bending Moment My is quite logical for me. (As far as I know they use the “Gesamtquerschnittsverfahren” described in EC 4)
But now I am struggling with the shear force Vz. Till now I always thought that the resistance of a composite beam was reduced to the shear force resistance of the steel joist (what in this case would be 2632 kN for a HEM 800)
This is clearly not the case. For this reason I assume, that the concrete brings in an additional load-bearing capacity.
So my questions are:

1. Why is this the case if there is no reinforcement at all
2. Is there any way to recalculate by hand the given values in the table?
3. Can I change something in the Input so that Sofistik just takes into account the “steel part”

Thank you very much!

Best regards

Aaron

Hi Aaron,

Can I change something in the Input so that Sofistik just takes into account the “steel part”

What you can do it to overwrite the plastic values via SV input

+PROG AQUA
SECT …
SV NPLC … NPLT … VYPL … VZPL … MTPL … MYPL … MZPL … MBPL … MT2P …

Is there any way to recalculate by hand the given values in the table?

The calculation of M,pl is difficult, because the concrete is not taken into account when under tension.
Because of this behaviour the sum of the inner forces is changing, then because of this the neutral/null line position changes, then because of this the tension area changes… and it repeats and repeats until equilibrium of inner forces is found.

For normal force Npl (steel) it is easy, you can use fy × Area for steel (approximate solution). In some cases, if the plates are under compression, then the reduction due buckling is also taken into account.

Why is this the case if there is no reinforcement at all

Currently concrete is taken into account for shear. One workaround would be to reduce the shear modulus of concrete but this can lead to convergence problems.

(after calculating the cross-section revert the shear modulus G to original value, you can do it via CTRL REST 3)

Regards,
STU

Thank you for your explanations!

I did it now with

STEU PLAS 0

Do you have also an idea how Vz ist calculated? Would be great!

Regards,

Aaron

Do you have also an idea how Vz ist calculated? Would be great!

Case: Calculation Vz and Vy for steel only

You can refer to Verification example DCE-EN13:

Case: Calculation Vz and Vy for steel+concrete
I will reply when I have more information. Currently I do not know exactly how concrete is taken into account.

Other examples can be found here: https://www.sofistik.de/documentation/2020/en/verification/

Regards,
STU

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