Tension Capacity of Very High Strength (VHS) Circular Steel Tubes after Welding

The details and results of an investigation into the tension capacity of very high strength (VHS) circular steel tubes after welding are presented. Two types of welded connections are used in the study: (1) complete penetration butt-welded VHS tubes, and (2) VHS tubes fillet welded to a steel plate along the whole perimeter of the tube. Both butt welded connections and transverse fillet welded connections failed in the heat-affected-zone (HAZ). The failure modes are compared with those of welded cold-formed square hollow sections. Significant strength reduction was observed in the HAZ compared with the strength of the VHS tubes. A strength reduction factor is proposed in this paper to modify the existing design rules. The FOSM (First Order Second Moment) reliability analysis method is used to calibrate the reduction factor. It seems that the tension member rules in the existing standards can be used along with the proposed reduction factors. The issue of matching between the parent metal and weld metal is also discussed.

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