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Steel Designers' Manual - 6th Edition (2003)
Chapter 26
Design of connections
by DAVID MOORE
26.1 Introduction
In general the cost of the design, fabrication and erection of the structural frame in
a steel framed building is approximately 30% of the total cost of construction. Of
these three items, fabrication and erection account for approximately 67%. Any
savings in the fabrication and erection costs can significantly reduce the overall cost
of construction. The majority of the fabrication costs are absorbed by the connections,
and the choice of connection also has a significant influence on the speed, ease,
and, therefore, the cost of erection. It is evident that the potential for reducing
the cost of steel construction lies in the suitable choice of the beam-to-column and
beam-to-beam connections. Indeed, because of the repetitive nature of connections,
even small material and labour savings in one connection can have an important
effect on the overall economy of the building.
In view of the significance of design and detailing it is remarkable that it is often
regarded as being of secondary importance in the design process. Current codes of
practice do little to redress this undesirable situation as many of them give little
guidance on connection design. Consideration of the local effects at connections is
usually left to the designer and this has led to a diversity of both connection types
and design methods. The traditional split of responsibilities, where the consultant
designs the members of the frame and the connections are designed and detailed
by the fabricator, has further compounded this problem.
Some of the many types of beam-to-column connections used in multi-storey steel
frame construction are shown in Fig. 26.1. Choice of connection type is usually based
on simplicity, duplication and ease of erection – all for economic reasons. Welded
joints provide full moment continuity but are expensive due to the on-site welding
involved. In recent years bolted connections have increased in popularity.They have
the advantages of requiring less supervision than welded joints, having a shorter
assembly time and support the load as soon as the bolts are in position. They also
have a geometry that is easy to comprehend and can accommodate minor discrepancies
in the dimensions of the beams and columns. However, when large forces are
involved, bolted connections can be criticized for requiring extensive space, which
may conflict with the architectural need for a ‘clean line’.
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