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 TM 5-684/NAVFAC MO-200/AFJMAN 32-1082
4-26. Distribution line metal poles.
and rusting. Although galvanizing may provide
good protection for many years, its effectiveness de-
Metal poles are generally of tapered tubular con-
pends a great deal on the climate and area contami-
struction with smooth or fluted surfaces. Attach-
nants. Towers should be inspected for rusting and
ments are made by bolting, clamping, or welding.
loose bolts. Spot painting is indicated for incidental
Steel poles are subject to rusting on all surfaces.
rusting, but complete paint coverage is necessary
There is little that can be done to reduce rusting on
where rusting is severe. Aluminum towers require
the inaccessible inside surfaces, beyond requiring
no painting, but bolts should be checked for tight-
that new poles be treated with a rust inhibitor and
ness. Tubular-type pole structures are preferred for
sealed to keep out moisture. When rust appears on
transmission lines, because they are more aestheti-
the outer surfaces, cleaning and painting are re-
cally pleasing than the lattice type.
quired. When corrosion at the ground line is severe,
additional protection may be provided by welding a
4-28. Pole-line metal hardware.
split ground sleeve over the affected area.
Pole-line hardware includes all metallic parts not
a. Aluminum poles. Aluminum alloy parts in con-
intended to be part of the current-carrying system,
tact with steel or other dissimilar metal require
except poles and other structures. This hardware is
painting, as may the steel surfaces. Aluminum sur-
generally of galvanized steel, although some items
faces embedded in concrete ordinarily need not be
may be aluminum alloy. The galvanized finish will
painted, unless exposed to extremely corrosive con-
resist corrosion for years under normal atmospheric
ditions.
conditions. Cleaning and painting may extend the
b. Self-weathering steel poles. It is important that
useful life; but, in general, little attention is neces-
all vegetation be kept away from these poles. Self-
sary except occasional checking for tightness. Be-
weathering steel, if kept moist, will corrode at a rate
cause the condition of bolts passing through other
equal to plain carbon steel, unless protected with a
items cannot be seen, replacement of a bolt is rec-
high quality paint system. Salt fogs cause an accel-
ommended if the head is rusted.
erated corrosion because the salt residue remains
on the pole. Self-weathering steel is not a com-
4-29. Painting of metal poles.
pletely maintenance-free material.
Preparation and painting of metal surfaces should
4-27. Transmission line metal towers.
comply with the SSPC painting manual, volume 1.
Special finishes should be treated in accordance
Towers are assembled of various structural compo-
with the manufacturer's recommendations. The
nents that are bolted, riveted, or welded in place
standard specifications for highway bridges of
into a lattice type construction. All surfaces are
AASHTOP Division 11.13.2 also provides data on
more or less accessible for cleaning and painting.
painting.
Most steel towers are galvanized to delay corrosion
Section VIII - CONCRETE POLES
4-31. Concrete pole foundations.
4-30. Concrete pole overview.
Reinforced and/or prestressed concrete poles have a
Other than for poles, the use of concrete in pole-line
projected life of 60 to 80 years and should require no
structures is limited almost entirely to the founda-
attention, except for replacement when damaged.
tions. Where used for metal structures, the founda-
Concrete poles are preferred under conditions
tion may often be reinforced and extend above
where the life of wood poles would be unduly short-
ground. Any small cracks should be filled with a
ened by decay or pests. When hauling concrete
high-strength grout. If substantial damage is found
poles, they must be secured so they cannot bounce.
on existing foundations, remove loose concrete,
Hard bouncing in transit will crack or chip the
clean surfaces, and restore the foundation to its
poles, especially when traveling over rough ground,
original size. For wood and concrete pole-line struc-
roads, or railroad tracks. Concrete poles also re-
tures, the backfill may be of concrete to provide
quire special attention if field drilling is required or
better bearing in soft soils, and may or may not be
there is a need for special banding or other attach-
visible at the surface. No maintenance is required.
ment methods. Poles setting depths may in some
For distribution structures, replacement concrete
cases be the same as wood poles, when the pole has
should normally be 3,000 pounds per square inch
been designed to be the equivalent of a wood pole of
(20,700 kilopascals) Class A.
the same class and length. Engineering personnel
should evaluate pole setting depths, guying, and
foundation requirements.
4-15
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