I just finished a design for an open web joist made out of square HSS (hollow structural sections). I notice that the diagrams in AWS D1.1 (god bless inter-library loan) detailing fillet weld fit ups always show a gap between the members to be joined. They don't dimension the gap but it's visually there.
Is this just their way of being clear in the drawings or should I really have a 1/16" gap or so? The particular page I'm talking about is p72 that has figure 3.2 on it "Fillet Welded Prequalified Tubular Joints Made by SMAW, GMAW, and FCAW". I was thinking maybe the gap would be the suggested way to avoid internal stresses developed as the weld cools (?)
Gory details: This HSS is the cold formed ASTM A500 grade B. The joist uses "stepped" connections --the webs more narrow than the chords, which enables the use of fillet welds. The both chords are 1/4" wall thickness, the webs are all 3/16" wall thickness. The web angle is
- The span is about 32 feet. The webs will be field welded completely around with 7018 in the horizontal position. They suggest chamfering the obtuse side of the web end to enable suffient throat.