80
mium for overtime wages and restoration services
which include damage assessment, cleanup, setup
of temporary equipment, design of the new facili-
60
ty, applying for federal and municipal approvals,
site preparation and, finally, reconstruction. Em-
ployees are sometimes laid off for months. In the
40
56 cases in which I have an estimated time for the
station's return to normal operation, the average
was 196 days and the standard deviation was 150
20
days. Three cases required more than 540 days to
return to normal operations, 16 cases required 300
or more days, and one station was bankrupted and
0
returned to the air under a different owner. The mon-
etary damage can be enormous.
The database currently contains damage esti-
mates for 73 of the 140 failures, which ranged be-
Figure 7. Histogram of factors leading to collapse.
tween 00 in 1959 to million in 1989, and
designed for. In general, whenever the wind was greater
averaged more than 3,000. The standard deviation,
than 10 mph, I concluded that wind was a factor, either
though, was more than
||content||
.5 million, indicating a large
by itself or in combination with the estimated iceload.
spread in the data, which can be attributed to 1) differ-
As shown in the Figure 7, 56% of the failures that could
ences in the types of costs that were accounted for, 2)
be categorized (60 of 106) were associated with com-
the wide range of sources from which the estimates were
bined wind-on-ice load. In 37% of cases (39 of 106),
obtained, 3) no attempt to adjust for monetary inflation,
I judged ice load alone to be the primary cause. In only
and 4) some cases that involved only a partial collapse
seven failures do I believe that severe wind was instru-
of the tower and therefore less damage. As one would
mental and that the ice load was incidental to the failure.
expect, costs increase with tower height and this rela-
tionship is shown in Figure 8. The wide range in the
2.5 Damage
estimated costs for all tower heights is best shown in
For each failure, I attempted to document the type
semi-log form.
and estimated cost of property and business losses,
Losses from a single tower failure have run as high
whether injuries occurred, how long each owner was
as million. Two 2000-ft television towers at the same
completely off the air, the percentage of original trans-
site outside Raleigh, North Carolina, fell approximately
mission area that was restored with a temporary anten-
1 hr apart in December 1989. Witnesses said that the
na, and how long it was before the station was finally
wind was calm and the sun had come out after a severe
operating normally.
sleet and freezing rain storm. When chunks of ice, some
When a tower falls, the initial damage usually includes
weighing an estimated 600 lb, began shedding from the
the complete loss of the tower and everything on it, and
warmed steel, reactional oscillations caused the heavily
often includes damage to the transmitter and electrical
loaded structures to buckle. An insurance industry source
feed housed at its base. Falling debris damages equip-
ment both on- and off-site, including commer-
8
10
cial and residential buildings, vehicles, electri-
cal transmission lines, and crops. In addition,
7
10
the costs to commercial and public broadcast-
ers accrue in the form of lost advertising reve-
nue until the station is able to return to the air.
6
10
The advertising rates that a station charges are
based on the size of its listening or viewing area.
5
10
This loss information is generally proprietary,
because of the highly competitive nature of the
104
industry. So important is maintaining market
share that owners need to return to the air as
soon as possible. This is usually done by install-
3
10
0
400
800
1200
1600
2000
ing a temporary, limited-coverage facility to
Tower Height (ft)
serve until a permanent one can be reconstruct-
Figure 8. Damage costs as a function of tower height.
ed. Getting back on air requires paying a pre-
8
Previous Page
