Page 42 - Handbook of Structural Steel Connection Design and Details

Fasteners and Welds for Structural Connections

Fasteners and Welds for Structural Connections 27

When the ambient temperature is below 0°F
When surfaces are wet or exposed to rain, snow, or high wind
When welders are exposed to inclement conditions
Surfaces and edges to be welded should be free from fins, tears, cracks,
and other defects. Also, surfaces at and near welds should be free from
loose scale, slag, rust, grease, moisture, and other material that may pre-
vent proper welding. AWS specifications, however, permit mill scale
that withstands vigorous wire brushing, a light film of drying oil, or anti-
spatter compound to remain. But the specifications require all mill scale
to be removed from surfaces on which flange-to-web welds are to be
made by submerged-arc welding or shielded metal-arc welding with
low-hydrogen electrodes.
Parts to be fillet-welded should be in close contact. The gap between
3
1
parts should not exceed ⁄16 in. If it is more than ⁄16 in, the fillet weld size
should be increased by the amount of separation. The separation
between faying surfaces for plug and slot welds and for butt joints land-
ing on a backing should not exceed ⁄16 in. Parts to be joined at butt joints
1
should be carefully aligned. Where the parts are effectively restrained
against bending due to eccentricity in alignment, an offset not exceed-
ing 10 percent of the thickness of the thinner part joined, but in no case
more than ⁄8 in, is permitted as a departure from theoretical alignment.
1
When correcting misalignment in such cases, the parts should not be
drawn in to a greater slope than ⁄2 in in 12 in.
1
For permissible welding positions, see Sec 1.3.4. Work should be posi-
tioned for flat welding whenever practicable.
In general, welding procedures and sequences should avoid needless
distortion and should minimize shrinkage stresses. As welding pro-
gresses, welds should be deposited so as to balance the applied heat.
Welding of a member should progress from points where parts are rel-
atively fixed in position toward points where parts have greater rela-
tive freedom of movement. Where it is impossible to avoid high residual
stresses in the closing welds of a rigid assembly, these welds should be
made in compression elements. Joints expected to have significant
shrinkage should be welded before joints expected to have lesser shrink-
age, and restraint should be kept to a minimum. If severe external
restraint against shrinkage is present, welding should be carried con-
tinuously to completion or to a point that will ensure freedom from
cracking before the joint is allowed to cool below the minimum specified
preheat and interpass temperatures.
In shop fabrication of cover-plated beams and built-up members, each
component requiring splices should be spliced before it is welded to
other parts of the member. Up to three subsections may be spliced to
form a long girder or girder section.

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