Page 99 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

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CONNECTIONS

CONNECTIONS 3.31

can be kept to a minimum. In the field, vertical and overhead welding sometimes may be necessary. The
best assurance of good welds in these positions is use of proper electrodes by experienced welders.
AWS D1.1 requires that only the flat position be used for submerged-arc welding, except for cer-
tain sizes of fillet welds. Single-pass fillet welds may be made in the flat or the horizontal position
1
5
in sizes up to / 16 in with a single electrode and up to / 2 in with multiple electrodes. Other positions
are prohibited.
When groove-welded joints can be welded in the flat position, submerged-arc and gas-metal arc
processes usually are more economical than the manual shielded metal arc process.
Designers and detailers should detail connections to ensure that welders have ample space for
positioning and manipulating electrodes and for observing the oper-
ation with a protective hood in place. Electrodes may be up to 18 in
3
long and / 8 in in diameter.
In addition, adequate space must be provided for deposition of the
required size of the fillet weld. For example, to provide an adequate
landing c, in, for the fillet weld of size D, in, in Fig. 3.19, c should be
5 3
at least D + / 16. In building column splices, however, c = D + / 16 FIGURE 3.19 Minimum land-
often is used for welding splice plates to fillers. ing for a fillet weld.
3.2.18 Welding Procedures
Welds should be qualified and should be made only by welders, welding operators, and tackers
qualified as required in AWS D1.1 for buildings. Welding should not be permitted under any of the
following conditions:
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 mate-
rial that may prevent proper welding. AWS specifications, however, permit mill scale that withstands
vigorous wire brushing, a light film of drying oil, or antispatter compound to remain. However, the
specifications require all mill scale to be removed from surfaces on which flange-to-web welds of
cyclically loaded girders are to be made.
Parts to be fillet-welded should be in close contact. The gap between parts should not exceed
3 / 16 in. If the gap is more than / 16 in, the fillet weld size should be increased by the amount of sepa-
1
ration. The separation between faying surfaces for plug and slot welds and for butt joints landing on
1
a backing should not exceed / 16 in. Parts to be joined at butt joints should be carefully aligned. Where
the parts are effectively restrained against bending due to eccentricity in alignment, an offset not
1
exceeding 10% of the thickness of the thinner part joined, but in no case more than / 8 in, is permit-
ted as a departure from theoretical alignment. When correcting misalignment in such cases, the parts
1
should not be drawn in to a greater slope than / 2 in in 12 in.
For permissible welding positions, see Art. 3.2.17. Work should be positioned for flat welding
whenever practicable.
In general, welding procedures and sequences should avoid needless distortion and should mini-
mize shrinkage stresses. As welding progresses, welds should be deposited so as to balance the
applied heat. Welding of a member should progress from points where parts are relatively fixed in
position toward points where parts have greater relative freedom of movement. Where it is impossi-
ble 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 shrinkage, and restraint should be kept to a minimum. If severe
external restraint against shrinkage is present, welding should be carried continuously 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.

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