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)
Fig. 5.2 Main bracing arrangements
K 'X' 2'
as part of the same operation. Where heavy-lift cranes are available much larger
segments of a tower can be erected but often even these are site bolted together.
Guyed towers provide height at a much lower material cost than self-supporting
towers due to the efficient use of high-strength steel in the guys. Guyed towers are
normally guyed in three directions over an anchor radius of typically 2 – 3 of the tower
height and have a triangular lattice section for the central mast. Tubular masts are
also used, especially where icing is very heavy and lattice sections would ice up fully.
A typical example of a guyed tower is shown in Fig. 5.3.
The range of structural forms is wide and varied. Other examples are illustrated
in Figs 5.4 and 5.5. Figure 5.4 is a modular tower arrangement capable of extension
for an increased number of antennas. The arrangement shown in Fig. 5.5 is adopted
for supporting flare risers where maintenance of the flare tip is carried out at ground
level.
A significant influence on the economics of tower construction is the method of
erection, which should be carefully considered at the design stage.
5.1.3 Environmental loading
Towers and masts 171
The primary environmental loads on tower structures are usually due to wind and
ice, sometimes in combination. Earthquakes can be important in some parts of the
world for structures of high mass, such as water towers. Loading from climatic temperature
variations is not normally significant but solar radiation may induce local
stresses or cause significant deflections, and temperatures can influence the choice
of ancillary materials.
Most wind codes use a simple quasi-static method of assessing the wind loads,
which has some limitations for calculating the along-wind responses but is adequate
for the majority of structures. Tower structures with aerodynamically solid sections
and some individual members can be subject to aeroelastic wind forces caused by
vortex shedding, galloping, flutter and a variety of other mechanisms which are