On that link,

drawn what I mean by reinforcing corners. Vertically.

Red area represents another 'object' to be dropped in where the welding points meet between walls/pillar.

that way, the vertical welds can be reinforced with another layer.

 

Horizontally, I suppse the welding machines can carry extra metal to reinforce the thickness of the welds, if necessary. Or a horizontal beam can be descended down, lock into the welded place by say indentations pressed on by a machine waiting by the tracks,
and that can be added as an extra layer...