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Steel Designers' Manual - 6th Edition (2003)
Chapter 5
Other structural applications
of steel
Edited by IAN DUNCAN with contributions from MICHAEL GREEN,
ERIC HINDHAUGH, IAN LIDDELL, GERARD PARKE,
JOHN TYRRELL and MATTHEW LOVELL
5.1 Towers and masts
5.1.1 Introduction
Self-supporting and guyed towers have a wide variety of uses, from broadcasting
of television and radio, telecommunications for telephone and data transmission
to overhead power lines, industrial structures, such as chimneys and flares, and
miscellaneous support towers for water supply, observation or lighting. These structures
range from minor lighting structures, where collapse might have almost no
further consequences, to major telecommunications links passing thousands of
telephone calls or flare structures on which the safety of major chemical plant can
depend. The term ‘mast’ describes a tower which depends for its stability on cable
guys.
5.1.2 Structural types
Steel towers can be constructed in a number of ways but the most efficient use
of material is achieved by using an open steel lattice. Typical arrangements for
microwave radio and transmission towers are shown in Fig. 5.1. The use of an open
lattice avoids presenting the full width of structure to the wind but enables the
construction of extremely lightweight and stiff structures. Most power transmission,
telecommunication and broadcasting structures fall into this class.
Lattice towers are typically square or triangular and have low redundancy. The
legs are braced by the main bracings: both of these are often propped by additional
secondary bracing to reduce the effective buckling lengths.The most common forms
of main bracing are shown in Fig. 5.2.
Lattice towers for most purposes are made of bolted angles. Tubular legs and
bracings can be economic, especially when the stresses are low enough to allow
relatively simple connections. Towers with tubular members may be less than half
the weight of angle towers because of the reduced wind load on circular sections.
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