Placing a rebar in the internal corner of composite sections (‘Γ’, ‘Ζ’ section etc) is optional because:
a) it does not significantly enhance the flexural strength since it is not placed in a section’s corner (tensile stresses appear at the external corners of the elements’ sections)
b) it does not increase the confinement because in case of an intense earthquake, where concrete spalling would occur, that rebar might buckle since it is not fully restrained.
c) in any case however, this corner rebar is useful from a construction point although it is not participating to the section’s confinement.