Presented at the 7th International Workshop on Atmospheric Icing of Structures (IWAIS'96),
Chicoutimi, Quebec, Canada, June 36, 1996
Atmospheric Icing and Tower Collapse in the United States
N. D. Mulherin
U.S. Army Cold Regions Research and Engineering Laboratory
72 Lyme Road, Hanover, New Hampshire, USA
of substandard material. However, most failures are
Abstract
CRREL has established a database of communica-
caused by rare natural events (for example, blizzard,
hurricane, tornado, and earthquake).
cellular, and so forth) that have occurred in the United
Ice storms are a natural hazard that cause towers to
States due to atmospheric ice accretion. The informa-
collapse. Ice can build up on towers from liquid precipi-
tion was compiled primarily from newspapers articles
tation such as freezing rain or drizzle, or from wet snow
and telephone interviews, but also from a multitude of
(precipitational icing), or from wind-transported, super-
other sources. The database currently lists 140 such
cooled fog droplets that freeze when they contact a struc-
failures of towers, ranging in height from 40 to 2000 ft
ture (in-cloud icing). Both types of icing are referred to
as atmospheric icing.
above ground level (agl), dating as far back as 1959.
For each case, I am compiling the following informa-
Atmospheric icing is a design consideration for the
radio and telecommunications industries. For optimum
tion: 1) structural characteristics of the tower, 2) the
signal transmission or reception, antennas are typically
geographic location and topography, 3) a description
elevated and exposed. These are prime conditions for
of the collapse, 4) concurrent weather, and 5) damage.
wind loading and ice accumulation. Ice buildup on tow-
The database is growing and therefore not fully anal-
ers causes signal interference, structural fatigue from
yzed. In many cases, data in all these topic areas do not
dynamic loading, guy wire stretch, ice-fall damage when
exist or are not available; some data I have yet to ob-
the ice sheds, and complete tower failure. This paper
tain. Trends in the current information are presented.
describes a database created at CRREL to document
icing-related tower failures in the United States. In this
Keywords
Communication tower, Glaze, Ice accretion, Icing,
context, a tower failure is defined as the collapse of
Radio and television, Rime, Tower collapse, Tower fail-
at least the antenna of a communication mast and
ure
can include the partial or total collapse of its supporting
tower.
1. Introduction
A radio or telecommunication mast is composed of
2. Sources of Information
1) an antenna, for sending or receiving electromagnetic
While catastrophic failure of a communication tower
is relatively rare, it occurs perhaps more often than is
cellular, etc., and 2) its supporting structure, one or more
generally known or acknowledged. There is no organi-
steel towers with guy cables and anchors (though some
zation that is responsible for maintaining a history of
towers are freestanding). This paper will use the term
tower failures, icing-related or otherwise. I assembled
"tower" to refer to both an antenna and its supporting
the information in this database over approximately a
structures as a unit.
decade of research, and believe it to be the most com-
While established engineering practice requires that
plete list of icing-related failures in existence. I was aid-
ed by individuals who shared with me their own unpub-
certain minimum loads be considered in their design,
lished lists of tower failures (Goudy 1992, Marshall 1992,
communication towers collapse for a variety of reasons.
Some collapses can be attributed to human error, such
Monts 1992, Laiho 1993). Their lists contained more
as flawed design or construction, lack of regular main-
well-known failures of towers throughout the world,
tenance, accidental damage, and so forth. Other causes
from any and all causes. Duvall (1993) provided a list
of 14 failures for which was known the maximum dis-
include malicious mischief, metal fatigue, and the use
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