Steel Designers Manual - TheBestFriend.org

This material is copyright - all rights reserved. Reproduced under licence from The Steel Construction Institute on 12/2/2007
To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/
Steel Designers' Manual - 6th Edition (2003)
Chapter 15
Columns and struts
by DAVID NETHERCOT
15.1 Introduction
Members subject to compression, referred to as either ‘columns’ or ‘struts’, form
one of the basic types of load-carrying component.They may be found, for example,
as vertical columns in building frames, in the compression chords of a bridge truss
or in any position in a space frame.
In many practical situations struts are not subject solely to compression but,
depending upon the exact nature of the load path through the structure, are also
required to resist some degree of bending. For example, a corner column in a building
is normally bent about both axes by the action of the beam loads, a strut in a
space frame is not necessarily loaded concentrically, the compression chord of a roof
truss may also be required to carry some lateral loads. Thus many compression
members are actually designed for combined loading as beam-columns. Notwithstanding
this, the ability to determine the compressive resistance of members is of
fundamental importance in design, both for the struts loaded only in compression
and as one component in the interaction type of approach normally used for beamcolumn
design.
The most significant factor that must be considered in the design of struts is buckling.
Depending on the type of member and the particular application under consideration,
this may take several forms. One of these, local buckling of individual
plate elements in compression, has already been considered in Chapter 13. Much of
this chapter is devoted to the consideration of the way in which buckling is handled
in strut design.
15.2 Common types of member
Various types of steel section may be used as struts to resist compressive loads;
Fig. 15.1 illustrates a number of them. Practical considerations such as the methods
to be employed for making connections often influence the choice, especially for
light members. Although closed sections such as tubes are theoretically the most
efficient, it is normally much easier to make simple site connections, using the
minimum of skilled labour or special equipment, to open sections. Typical arrangements
include:
402