In SHAPE-THIN, I want to connect a free-standing cross-section part by means of a null element with the rest of the cross-section. Graphically, this is no problem.
For the calculation, however, SHAPE-THIN always asks to specify a thickness t* for the shear calculation.
In chapter 7.2.1. of the SHAPE-THIN manual, you can find the equations for the shear areas and the Bredt torsional constant. Here, the element thickness t* is in the denominator so that the division by 0 would be a problem. For "free-standing" elements, you therefore have to specify a user-defined equivalent thickness, for expamle the thickness of one of the connecting elements.
Select the null element and in the "Edit Member" dialog box select the "Effective thickness for shear transfer" check box. The text box for thickness t* becomes available. Now the calculation is possible.