Page 29 - Handbook of Structural Steel Connection Design and Details

Fasteners and Welds for Structural Connections

14 Chapter One

1.3 Welded Connections

Welded connections are used because of their simplicity of design, fewer
parts, less material, and decrease in shop handling and fabrication oper-
ations. Frequently, a combination of shop welding and field bolting is
advantageous. With connection angles shop-welded to a beam, field con-
nections can be made with high-strength bolts without the clearance
problems that may arise in an all-bolted connection.
Welded connections have a rigidity that can be advantageous if prop-
erly accounted for in design. Welded trusses, for example, deflect less
than bolted trusses, because the end of a welded member at a joint
cannot rotate relative to the other members there. If the end of a beam
is welded to a column, the rotation there is practically the same for
column and beam.
A disadvantage of welding, however, is that shrinkage of large welds
must be considered. It is particularly important in large structures
where there will be an accumulative effect.
Properly made, a properly designed weld is stronger than the base
metal. Improperly made, even a good-looking weld may be worthless.
Properly made, a weld has the required penetration and is not brittle.
Prequalified joints, welding procedures, and procedures for qualify-
ing welders are covered by AWS D1.1, Structural Welding Code—Steel,
American Welding Society (2006). Common types of welds with struc-
tural steels intended for welding when made in accordance with AWS
specifications can be specified by note or by symbol with assurance that
a good connection will be obtained.
In making a welded design, designers should specify only the
5
amount and size of weld actually required. Generally, a ⁄16-in weld is
3
considered the maximum size for a single pass. A ⁄8-in weld, while only
1 ⁄16-in larger, requires three passes and engenders a great increase in
cost.
The cost of fit-up for welding can range from about one-third to sev-
eral times the cost of welding. In designing welded connections, there-
fore, designers should consider the work necessary for the fabricator and
the erector in fitting members together so they can be welded.

1.3.1 Types of welds
The main types of welds used for structural steel are fillet, groove, plug,
and slot. The most commonly used weld is the fillet. For light loads, it
is the most economical, because little preparation of material is required.
For heavy loads, groove welds are the most efficient, because the full
strength of the base metal can be obtained easily. Use of plug and slot
welds generally is limited to special conditions where fillet or groove
welds are not practical.

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