Connections in trusses
Truss connections
are generally welded, except for site splices.
The connections
between the members of a truss were traditionally bolted but welded connections
are now preferred, especially in tubular construction. Nevertheless it may be
necessary to introduce splices in the chord members if the complete trusses are
too long for transportation. These splices provide for bolting individual
lengths of trusses on site and should be located and detailed carefully if they
are architecturally important.
Connections in
open section trusses are lapped and welded.
Traditional truss
construction based on open sections (angles and tees) used bolts and gusset
plates. The position of the bolts was usually detailed to minimise
eccentricities. In welded construction the internal members are typically
attached directly to the top and bottom chords. These chords are usually
continuous except at changes of direction or where splices are necessary to
reduce the length of the assembly for transportation. Internal members lap onto
the chord members and are simply connected by fillet welding.
Connections in
trusses using heavier sections are welded but may require more careful
preparation.
Long span or
heavily loaded trusses often use I, H or channel sections. Internal members are
generally cut to fit directly against the flanges of the chord members and are
profile welded to form the connection.
Connections in
tubular trusses are usually welded.
Tube to tube
joints, such as those in tubular trusses, are usually welded, because full
profile welded joints not only look better but are also cheaper than creating
elaborate bolted joints. It is usually cheaper to make truss connections if the
chords are made from rectangular tubes, rather than circular. This is because
the ends of the diagonals can be straight cut, rather than cut to the more
complex intersection profile if circular chords are used. In either case the
end of the diagonal may be cut in the same plane as the chords if a fillet weld
is adequate. This will normally be adequate, but if a butt weld is needed the
end of the diagonal must be properly prepared. A number of fabricators use
profiling machines which automatically cut the diagonal to the correct line and
end preparation for welding.
Welded
connections for tubular trusses
Intersecting
angles should not be too small.
It is important
that the truss geometry does not produce too small an intersection angle
between members. The limit is about 30 degrees for rectangular hollow sections
and 20 degrees for circular hollow sections, and below this value it is
difficult to get the welding electrode in to make a weld.
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