Unzipping connection behaviour is not referred to in EN 1994-1-1 - only ductile and non-ductile shear connections are classified. It might be clear that unzipping connections belong to the non-ductile ones, but not all the non-ductile connections are unzipping ones. Characteristic of unzipping connection behaviour is that, initially, connection stiffness is high and composite action is efficient. However, as the load increases, so the connection loses its shear stiffness very rapidly, and after the onset of plastic behaviour in the beam, the decking no longer contributes to the bending resistance of the initially composite member. This behaviour is most typically seen in shallow floor beams (abbreviated to SF beams) supporting hollow-core decking. This is a companion paper to the one in which the composite action in SF beams with ductile shear connections is discussed.