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.

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.