This paper describes tests on various types of knee joints for steel portal
frames constructed from cold-formed rectangular hollow sections (RHS) to e
xamine the ability of the connections to form plastic hinges. Welded stiffe
ned and unstiffened knee joints, bolted knee joints with end plates, and co
nnections with a fabricated internal sleeve were included in the experiment
al investigation. Most connections tested under opening moment failed by fr
acture in the heat-affected zone of the RHS near the weld. The connections
tested under closing moment failed by web local buckling, which occurred ne
ar the connection. While the stiffened and unstiffened welded connections s
atisfied the strength interaction requirements in the available design guid
es, the connections did not maintain the plastic moment for sufficiently la
rge rotations to be considered suitable for a plastic hinge location. The u
nstiffened welded joints were not able to reach the plastic moment. The use
of an internal sleeve moved the plastic hinge in the connection away from
the connection center-line and reduced the stress on the weld between the l
egs of the connection. It was found that sleeve connections were capable of
sustaining the plastic moment for large rotations considered suitable for
plastic design.