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Steel Designers' Manual - 6th Edition (2003)
Chapter 14
Tension members
by JOHN RIGHINIOTIS and ALAN KWAN
14.1 Introduction
Theoretically, the tension member transmitting a direct tension between two points
in a structure is the simplest and most efficient structural element. In many cases
this efficiency is seriously impaired by the end connections required to join tension
members to other members in the structure. In some situations (for example, in
cross-braced panels) the load in the member reverses, usually by the action of wind,
and then the member must also act as a strut. Where the load can reverse, the
designer often permits the member to buckle, with the load then being taken up by
another member.
14.2 Types of tension member
The main types of tension member, their applications and behaviour are:
(a) open and closed single rolled sections such as angles, tees, channels and the
structural hollow sections. These are the main sections used for tension
members in light trusses and lattice girders for bracing.
(b) compound sections consisting of double angles or channels. At least one axis of
symmetry is present and so the eccentricity in the end connection can be minimized.
When angles or other shapes are used in this fashion, they should be
interconnected at intervals to prevent vibration, especially when moving loads
are present.
(c) heavy rolled sections and heavy compound sections of built-up H- and box sections.
The built-up sections are tied together either at intervals (batten plates)
or continuously (lacing or perforated cover plates). Batten plates or lacing do
not add any load-carrying capacity to the member but they do serve to provide
rigidity and to distribute the load among the main elements. Perforated plates
can be considered as part of the tension member.
(d) bars and flats. In the sizes generally used, the stiffness of these members is very
low; they may sag under their own weight or that of workmen.Their small crosssectional
dimensions also mean high slenderness values and, as a consequence,
they may tend to flutter under wind loads or vibrate under moving loads.
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