The most commonly used guyed towers are
fabricated from steel in untapered sections 10 to 20
feet long. These constant dimensional sections are
erected one above the other to form the desired height.
Structural stability for this type of tower is provided
by attaching guy wires from the tower to ground
Base supports for guyed towers vary according to
the type of tower to be installed. Three commonly used
base supports are the tapered tower base, the pivoted
tower base, and the composite base. All three are
shown in figure 8-30.
A tapered tower base concentrates the load from
multiple tower legs to a small area on the foundation.
Freestanding, or self-supporting, steel antenna
towers are characterized by heavier construction than
guyed towers and by a shape that tapers in toward the
top from a wide base. Freestanding towers exert much
greater weight-bearing pressure on foundations than
most guyed towers. Consequent y, deeper foundations
are required (because of the greater size, the weight,
and the spread of tower legs) to provide sufficient
resistance to the uplift. Each leg of a freestanding
tower must be supported by an individual foundation.
Figure 8-31 shows a typical individual foundation for
a freestanding tower, and figure 8-32 shows a
foundation plan for a triangular steel freestanding
tower. Bracing and material specifications for these
towers are the same as for guyed towers.
The pivoted base is used primarily on lightweight
structures for ease of tower erection.
A composite base is generally used with heavier
towers because it affords much greater supporting
strength than the other two types.
Sections for lightweight towers are usually
assembled before delivery, to expedite final tower
assembly, whereas heavier weight towers must be
assembled completely in the field.
Tower bracing should include diagonal bracing
and horizontal struts in the plane of each tower face
for the full tower height.
Advance planning for tower assembly and
erection is essential for completion of the project
safely and correctly. Both the installation plan and the
manufacturers instructions should be studied to gain
a complete understanding of the tower assembly and
erection methods to be used. The following general
procedures and practices should be observed for the
assembly and erection of towers:
1. Assemble the tower sections on well-leveled
supports to avoid building in twists or other deviations.
Any such deviations in one section will be magnified
by the number of sections in the complete assembly.
Figure 8-30.Base support for guyed towers.