Testing of small rectangular hollow sections having welded connections

A testing program has been carried out by MWD with the aim of comparing imported hot-rolled and New Zealand-made cold-rolled RHS with welded connections at location of maximum bending. A full description of the experiments is found in Ministry of Works and Development Central Laboratories Report No. 5-80/3. This is available from the Ministry of Works and Development Head Office Library. The size of section compared was 102 x 51 x 4.9 mm corresponding to the largest size manufactured by New Zealand Steel Limited. Lengths of RHS of respective types were fabricated into 1.83 m long simply supported beams with a fillet-welded dividing plate through the midspan location. Two such beams of the cold-rolled and hot-rolled RHS were loaded monotonically through application of load at the dividing plate. The cold-rolled beams failed at a rather low maximum deflection ductility of 7.3 and in a manner which indicated a lowered yield stress in the vicinity of the weld of the dividing plate. On the other hand, the hot-rolled beams continued to strain harden to the limit of the test rig, equivalent to a deflection ductility of 29. While hysteretic testing is needed to draw firm conclusions
on the reliability of cold-rolled RHS in energy-absorbing systems, the test series does permit the observation that the material would be inadmissible in a situation where moderate to large member ductility demands were anticipated near welds.