Introduction

The function of a connection is to make an effective attachment between individual elements.

Connections are clearly needed where two different members meet, for example at the end of a beam supported by a column. They are also required to join individual lengths, for example of column where the building height exceeds the longest sections available. The same is true for any large scale structural component since there is a limit on the length and weight which can be transported from the steel mill to the fabricator's shop, be handled in the shop, and then be transported to site and lifted into position by crane.

It may be also be desirable (but not necessarily economical) to vary the section size to suit particular loading conditions - for example the upper sections of a column will often be smaller than the lower sections.

Connections must also transfer the forces safely between the connecting elements.

Connections not only secure the ends of elements where they meet, but also transfer bending moments, shear forces, compressions and torsions (twisting effects) between the members. To design a structural connection, it is necessary to follow the loads from one member to the other, and ensure that at every section, stresses are safe.

Common connection types

The use of a limited range of standard connections within a project can improve construction efficiency significantly.

The fabricator is often responsible for the design of connections. Details are therefore generally designed to suit individual working practices. However there have been significant developments towards standardisation, and preferred details have been established for connections between universal sections in rectilinear frameworks used predominantly for multi-storey construction. The adoption of standard connections makes design, fabrication and erection more efficient, and reduces the chances of errors. Using a standard bolt size saves fabrication time because drill bits do not need to be changed.

Where standard connections are not appropriate it may still be possible to adopt some standardisation for the particular project. In doing so the number of different connection details should be limited, and, if possible, a single bolt type (grade, diameter and length) used. Fully threaded bolts have become popular because a single length can be used for a range of plate thicknesses.