The tension and compression zones of moment plate connections were studied separately by testing branch plate and hollow structural section connections under each type of loading. Square hollow section flanges were reinforced by doubler plates fillet-welded all around. The results from 13 specimens tested in tension indicate that branch plate to reinforcing plate width ratio is an important parameter in joint behaviour. The dominant failure mode was punching shear of the reinforcing plate. The importance of reinforcing plate and HSS wall thicknesses was apparent from the results of 13 specimens tested in the compression series. The capacities of specimens in all but one test in this series were limited by failure of the HSS webs.Key words: hollow structural sections, W-shape, columns, beams, connections, experimental, design, steel.