Mount Wellington Unique broadcasting tower
Recognised text
Text below was produced by optical character recognition and may contain errors. Check it against the original.
| MQUNT WE
UNIQUE BROAD?
As part of equalisation ir 1
ing tower is being constructec
on Mt Wellington, overlookin
replace the existing lattice st
withstanding the extremes o
deriving from the “Roaring Fq'w
The new tower has b
Broadcasting to suit the neecs
ment. It will consist of a fully's
section with a non-uniform ver
and a radome-enshrouded iat
column from 67m up to approx
to support Band 1, Band 2 zan
and the local radio comm
Provision is being made to enz
from the same aperture as t
will be circular in cross-secticn
be fitted with tuned liquid damy
wind-induced dynamic moticn
this tower have been derived
in maintaining the existing tow
The existing tower was bull
by Johns & Waygood Ltd, to
array. During the following 1
damage due to falling ice. Th¥
lem with a degraded broadcza
mon during winter, and st
required during summer. By!
array had reached the end 2
replacement array was plarre
ter protective radome. Tower
tion and radome construction¢
mer of 1979-80 and was final
mer of 1982-83. Included »
extension to the tower to s
within a 2.0m diameter radome
antenna was added within ¥
broadcast SBS television.
Although the radome wzs
damage to the antennas, it =%
ated with wind-induced dy==
tower. This led to an on-gomg
ticularly associated with bo®==
tower. The fitting of tunec ‘&
tower in 1992 has helpec =
problems. Ice damage to &1
tower continues and maini=s
the frequent occurrence of =&
The existing tower a"—:_z
capable of being satisfact=
additional television and FMH
broadcast. This in conjuncie®
nance requirements formas ¥
struction of a replacement ¥%
mental work to this enc =4
Following an extensive em&=
including public forums, ™= &
the new tower was finaises &
presented to the Hobart & =
in February 1993. Afier =
Formwork and reinforcemerit set up prior to pouring foundation ring beam. cratic process, plannnc
10 — The Broadcaster, July 1994
| MOUNT WEEEINGTON ]
i»
UNIQUE BROADCASTING TOWER ¢
y
{
’
{
As part of equalisation ir Tasmania, a new broadcast- »
ing tower is being constructed at 1252m above sea level
on Mt Wellington, overlooking Hobart. This tower is to
replace the existing lattice steel tower, which has been
withstanding the extremes of the snow, ice and winds
deriving from the “Roaring Fq"ties” for the last 34 years.
The new tower has been designed by Telecom
Broadcasting to suit the neecs of the site and the environ-
ment. It will consist of a fully‘enclosed reinforced concrete
section with a non-uniform vertical taper up to 67m height,
and a radome-enshrouded iatticed steel antenna support
column from 67m up to approximately 130m. The tower is
to support Band 1, Band 2 and Band 4/5 antenna arrays,
and the local radio communication requirements.
Provision is being made to enable broadcasting on Band 3
from the same aperture as the Band 2 array. The tower
will be circular in cross-section over its total height and will
be fitted with tuned liquid dampers to absorb the energy of
wind-induced dynamic moticns. Many of the features of
this tower have been derived ~om the experience gained
in maintaining the existing tows
The existing tower was built in the summer of 1959-60
by Johns & Waygood Lid, to support the ABT-2 antenna
array. During the following winter it suffered extensive
damage due to falling ice. This became an on-going prob-
lem with a degraded broadcast signal being not uncom-
mon during winter, and siructural repairs frequently
required during summer. By the late 1970’s the antenna
array had reached the end of its serviceable life and a
replacement array was plarre zlong with a 7.6m diame-
ter protective radome. Tower _grading, antenna installa-
tion and radome construction commenced during the sum-
mer of 1979-80 and was finaly completed during the sum-
mer of 1982-83. Included in this work was a 12m high
extension to the tower to supgort an FM antenna array
within a 2.0m diameter radome. 2 single channel UHF slot
antenna was added within the 2and 1 radome in 1986 to
broadcast SBS television.
Although the radome was successful in stopping ice
damage to the antennas, it = =*=d other problems associ-
ated with wind-induced dynamic excitation of the whole
tower. This led to an on-goinz maintenance problem, par-
ticularly associated with boltec connections throughout the
tower. The fitting of tuned fawid dampers high up in the
tower in 1992 has helped =cuce the vibration-related
problems. Ice damage to the 2oen latticed sections of the
tower continues and maintenance is difficult because of
the frequent occurrence of ind=ment weather.
The existing tower anc 'j 2ntenna systems are not
capable of being satisfacto™d: upgraded to support the
additional television and FM "0 services required to be
broadcast. This in conjunct™ with the significant mainte-
nance requirements formec T justification for the con-
struction of a replacement ®=%=7. Planning and develop-
mental work to this end £272d in December 1991.
Following an extensive envi=™™antal impact assessment
including public forums, the 2¥%eral form and location of
the new tower was finalise< =< “wo variations of this were
presented to the Hobart C = ===ncil for planning approval
in February 1993. After 2 7 == of steps in the bureau-
cratic process, planning ==="- = was granted in July,
S
Tv
TING TOWER
gne 2 new broadcast-
252 z2bove sea level
p=rt. This tower is to
pwer. which has been
snow, ice and winds
for Te last 34 years.
s gned by Telecom
& s%2 and the environ-
g=c reinforced concrete
=per up to 67m height,
st=el antenna support
g% 130m. The tower is
= §
mc 45 antenna arrays,
2tion requirements.
woadcasting on Band 3
nc 2 array. The tower
r #s total height and will
o absorb the energy of
fzny of the features of
the experience gained
he summer of 1959-60
jort the ABT-2 antenna
ir it suffered extensive
:2me an on-going prob-
gnal being not uncom-
rzl repairs frequently
zte 1970’s the antenna
serviceable life and a
ong with a 7.6m diame-
ading, antenna installa-
nenced during the sum-
npleted during the sum-
work was a 12m high
{ an FM antenna array
single channel UHF slot
'd 1 radome in 1986 to
cessful in stopping ice
| other problems associ-
excitation of the whole
intenance problem, par-
nections throughout the
dampers high up in the
e the vibration-related
1 latticed sections of the
2 is difficult because of
nt weather.
tenna systems are not
Jgraded to support the
services required to be
h the significant mainte-
ustification for the con-
Planning and develop-
d in December 1991.
ntal impact assessment
ral form and location of
/0 variations of this were
icil for planning approval
r of steps in the bureau- e
al was granted in July, Alimak personnel access hoist guide frame attached to the tower.
The Broadcaster, July 1994 — 11
1993 and Federal Parliamentary funding approval was
granted in December, 1993.
The primary loading for the design of the tower is wind
loading, and this has been derived from Bureau of
Meteorology wind data recorded on the Mt Wellington
Broadcasting Site over a number of years. These wind
loading parameters confirm Mt Wellington’s reputation of
being a very windy place.
The new tower is to be constructed in two stages over
two summer seasons. Stage 1 consists of the reinforced
concrete section up to RL 67m and the associated internal
access and cable runway steelwork. Stage 2 is to include
the lattice steel support column, the antenna arrays, tuned
liquid dampers and the radome.
The design of the tower has included a dynamic analy-
sis to determine the tower’s sensitivity to wind excitations
in both the along-wind and cross-wind directions.
Specially designed Tuned Liquid Dampers will be installed
at two levels high up in the tower to absorb the energy of
any wind-induced movement, particularly in the vicinities
of the fundamental natural frequencies of the tower. This
will be beneficial to the tower serviceability deflection
requirements and to the long-term fatigue life of the struc-
tural components.
The design of Stage 1 was sub-contracted to the con-
sulting engineering group Structural Mechanics &
Dynamics. They have also been awarded the design and
supply of the Tuned Liquid Dampers. A contract for the
construction of the Stage 1 was let in December 1993 to
Concrete Constructions (Tasmania). Construction com-
menced in January 1994 with the excavation of the foun-
dations and pouring of blinding concrete, approximately
90 cubic metres of which was used to replace significant
clay seams in the foundation rock. The ring beam was
then anchored to the bedrock by 18 rock anchors at
depths varying between 10 and 15 metres. Each of these
were post-tensioned to 2000 kN (= 200 tonnes).
The tower shaft was poured using a specially designed
slipform. The slipform was based on a Swedish design,
incorporating the ability to reduce in diameter and vary the
wall thickness and slope. This occurred while constantly
moving upwards at an optimum rate of approximately
200mm per hour. It was assembled on the ring beam and
after tests and adjustments, the concrete pour com-
menced on 23 March. Due to some technical problems
and the frequent intervention of the weather, the slipform-
ing period was extended from 3 weeks to approximately 8
weeks.
Although it was scheduled to operate continuously 24
hours per day for up to 6 days the regular occurrence of
high winds, snow and icing frequently made shut-downs
necessary, particularly in the latter stage of the slipforming
operation. Construction work often continued in the poor
weather conditions until a stoppage was forced by the
wind speed exceeding the maximum operating speed of
the Alimak personnel access hoist.
The tower is to be temporarily capped during the winter
period and the internal access ladders and cable runway
steelwork is to be installed before the commencement of
Stage 2 of the construction, scheduled for November
1994.
TOM GLASS
Slipform at RL49m and progressing upwards.
T
12 — The Broadcaster, July 1994
R A——