This article and the linked example address a topic not addressed by the Eurocodes and NTC except for structural elements hinged at the ends and subject to axial compression only.

The approach to the verification of press-flexed calastrated composite elements subject to both axial compression and bending in the two principal planes in addition to axial compression can be the same as that described by the standards for profiles with bi-symmetrical cross-sections provided with cores in the two bending planes as long as the connections between the profiles have "sufficient stiffness" and symmetry such that the homogeneous behavior of the section is considered to be homogeneous to the effects of both axial compression and bending.

Composite element calastrated press-flexed