T shaped cross-section

Hey,

I have a question about modelling a "T" shaped cross-section through an "I" shape inside the "cross sections (Karamba)" component. I modelled the shape by setting the lower flange thickness and width to zero but it seems the cross-section properties are calculated incorrectly. Could it be that the "I" cross-section is only meant to be used with thin-walled elements such as steel I profiles?

To understand this better I went one step back and tried comparing a rectangular cross-section modelled with the "trapezoidal" and "I" shaped inputs. As previously mentioned, I omitted the flanges to get a rectangle out of the "I" shape. 

The results I get can be seen in the figure bellow. Incorrect are the shear areas in Y (AreaY) and Z (AreaZ) direction as well as the torsional moment of inertia (Ipp) and consequently the torsional resistance moment (Wt).

Cross-section is a massive rectangular section of 200cm width and 100cm height.

I understand, there is a component for modifying the section properties of a cross-section with which I could correct the wrong values, but this obviously has to be done manually. If someone knows the expressions behind the calculations for the shear areas and the torsional moment which I could input into my script to modify these automatically that would be great. 

Thanks (and sorry for the long description),
Matej