Application of large heat input automatic welding process to beam-to-column connections of steel framed structures (1st Report)

Summary

Beam-to-column connections of construction steelwork have been conventionally welded by a CO₂-based, semi-automatic, multi-layer welding process. Such welding processes, however, face the problems of limited efficiency and the fact that the welding quality often depends on the welder's workmanship.

The electrogas arc welding process is generally considered difficult to apply to beam-to-column connections of construction steelwork because of the poor weld toughness it confers due to its conventional high heat input. Based on recent developments in structural steel plates for large heat input welding, the authors have developed a one-pass vertically upward large heat input electrogas arc welding process (referred to in this paper as large heat input welding process and in the diagrams as EGW) able to produce welds with a deposition rate of twice the conventional one without any loss of toughness and with far fewer weld defects. The proposed process can also be applied to new improved seismic details, such as non-scallop details, etc. A key characteristic of the newly developed welding process is that stable penetration can be obtained even when heavy-gauge plates are being welded through the welding torch being moved as a trapezoid within the groove formed by a water-cooled copper shoe.

The heat input in the proposed welding process is some 5–20-fold greater than that conventionally applied, but the newly developed construction steel plates for large heat input welding show Charpy impact values in both the weld metal and the heat affected zone (HAZ) of not less than 150 J (zero °C). The Charpy impact test results further suggest that, even when the developed steel is welded by the proposed large heat input welding process at a plate thickness of 25 mm, the weld fracture toughness properties of 150 J at zero °C can be maintained, achieving a performance equivalent to that found during CO₂ welding of conventional 25 mm thick steel.