Calculation of MAT2 properties from PCOMP

[pbd999]

When modeling a composite laminate using MSC.Nastran the PCOMP and MAT8 (or MAT1) entries are converted before the run to an equivalent PSHELL and four MAT2 entries which are used in the actual Nastran run. I understand that three of these MAT2 cards are calculated from classical lamination theory.

MID1 MAT2 = [A]/t -> membrane
MID2 MAT2 = [D]/(t^3/12) -> bending
MID4 MAT2 = -/t^2 -> coupling

Now my question: How are the values in the MAT2 associated with MID3 (transverse shear) calculated? I haven't been able to find this info anwhere....

Thanks alot.