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310 Barry’s Advanced Construction of Buildings
sizes being used at heavily loaded connections. Fillet welds of up to 10 mm are formed by
one run of the filler rod in the arc welding process and the larger welds by two or more
runs, as illustrated in Figure 5.32. When filled welds are specified by leg length, the steel
fabricator has to calculate the gauge of the filler rod and the current to be used to form the
weld. An alternative method is to specify the weld as, for example, a 1–10/225 weld, which
signifies that it is a 1 run weld with a 10 gauge filler rod to form 225 mm of weld for each
filler rod. As filler rods are of standard length, this specifies the volume of the weld metal
used for the specified length of weld and therefore determines the size of the weld. Intermittent
fillet welds are generally used in structural steelwork, common lengths being 150,
225 and 300 mm.
Butt welds
These welds are used to join plates at their edges. The weld metal fills the gap between
them. The section of the butt weld employed depends on the thickness of the plates to be
joined and whether welding can be executed from one side only or from both sides. The
edges of the plates to be joined are cleaned and shaped as necessary, the plates are fixed in
position and the weld metal run in from the filler rod. Thin plates up to 5 mm thick require
no shaping of their edges and the weld is formed as illustrated in Figure 5.33. Plates up to
12 mm thick have their edges shaped to form a single V weld as illustrated in Figure 5.34.
The purpose of the V-section is to allow the filler rod to be manipulated inside the V to
deposit weld metal throughout the depth of the weld without difficulty. Plates up to 24 mm
thick are joined together either with a double V weld, where welding can be carried out
from both sides, or by a single U where welding can only be carried out from one side.
Edges of plates
brought together
for welding
Penetration
Deep penetration butt weld formed
by welding from both sides
Downhand weld
Penetration
Sealing run
Downhand butt weld
Figure 5.33 Butt welds.