Engineering Report
Çanakkale Antenna Tower
Ian Ritchie Architects & Arup
Structural Report
The brief
The brief calls for the design of an antenna tower for broadcasting and of spaces supporting
ancillary facilities open to public use. The competition is considered as a quest for design
excellence and aims to ensure development of cultural, artistic, scientific, ethical and
environmental values through economical, functional and innovative solutions. The design
concepts to be developed are expected to achieve innovation, creativity, originality and
identity while optimizing functionality and connectivity to its immediate surroundings.
Design precedents
Towers such as the Eiffel Tower in Paris and many microwave towers worldwide use a
tapering steel lattice structure. As an alternative, there is the guyed mast, of which many have
been built to carry antennae systems to great heights. A notable example is the Torre de
Collserola, engineered by Arup for the Barcelona Olympic Games of 1992
Arup has more recently been involved in the design of air traffic control towers at London’s
Heathrow Airport and at Istanbul’s Sabiha Gökçen Airport. These are 87m tall and 110 m tall
respectively, and both have contributed to the design thinking of the Çanakkale Antenna
Tower. At Heathrow, the use of a cable-stayed steel tower allowed the mast diameter to be
reduced to approximately half of that of an equivalent cantilever mast. At Sabiha Gökçen, the
constantly varying profile of the tower, combined with alternating solid-void cladding
patterns, disrupt the wind and prevent the formation of wind vortices which cause cross-wind
oscillation (a significant problem for tall slender structures), which are normally resisted by
complex damper systems. In addition, base isolation reduces the seismic forces in the
structure by 60%.
A new concept
For the Çanakkale Antenna Tower Ian Ritchie Architects and Arup have developed a
structural system which minimises both the wind and seismic loads to be carried by the
structure. It integrates in the most minimal way the requirements of the brief with a structural
system which carries both the lateral and vertical loads of the antenna tower and the other
accommodation.
Primary structure
The primary structure is very simple. A slender steel lattice mast rises from the roof of the
lower level accommodation and supports access platforms and antennae. The mast is
braced/guyed to the roof of the lower level accommodation by cables made of Kevlar K49
fibre that lie in the surface of the conical fabric sheath that wraps around the tower. The lower
level accommodation is constructed of reinforced concrete, with internal walls and columns
supporting the weight of the tower. This reinforced concrete structure sits on seismic base
isolators on top of simple reinforced concrete footings which are founded on the sandstone.
Base isolation has been chosen because it provides a number of significant benefits:
 Reduces oscillation
 Dissipates energy of earthquake
 Reduces forces in structure
 Protects non-structural elements
To maintain stiffness during strong winds, the primary structure is prestressed by tensioning
the principal guys, so that the downwind guys do not go slack.
Mast
As a fundamental part of the structure, the mast carries the entire weight of the tower, plus the
precompression resulting from the guy prestress, and resists torsional, wind and seismic
effects, with help from the principal guys. From about 3.5m diameter at its base, it tapers to
about 1.5m diameter at the highest access platform. An enclosed helical stair and two
passenger lifts sit outside the central mast to provide access to the public and fire observation
decks.
The steel mast is of small enough diameter to be prefabricated and transported to site in 12 m
or longer lengths completely fitted out with stairs/ladders, and electrical risers. Offsite
prefabrication will help ensure high quality, speed construction, and minimise the amount of
hazardous work at height needed to construct the tower.
Preliminary calculations indicate that the mast can be constructed of tubular steel and will
weigh on average about 750kg/m vertically. Vertical members will typically be about 200mm
wide and bracing members about 110mm wide.
Guys
The main guys, which sit in the surface of the fabric sheath that wraps the tower, are made of
polyurethane-coated Kevlar K49 fibre cables. This material has been chosen because, thanks
to its low dielectric properties, it is nearly invisible to broadcast signals, and typical guy line
interference can be mitigated. The material has excellent fatigue performance, about half the
stiffness of steel, and very high strength. The insulation properties also reduce potential for
arcing, galvanic corrosion, and electrical safety hazards. Preliminary calculations, assuming
six primary guys at 60° intervals in plan, indicate cable diameters of about 150mm.
We anticipate full-scale testing of the guys and their connections will be carried out by the
manufacturer.
Seismic design
The client response to one question from a competitor says states that ‘there is not a particular
expectation for post-earthquake use’ but the Turkish Seismic Code requires an importance
factor of I=1.5 (the highest) for ‘other telecommunication facilities’, indicating that it
classifies them under the building groups which should remain operational after a design
earthquake. At this stage we have assumed that the Çanakkale Antenna Tower is classified as
‘other telecommunication facilities’. This is critical as an importance factor of 1.5 means a
direct increase in seismic forces of 50%.
Wind engineering
The exposed location and local topography will generate significant wind forces on the fabric
wrapping, the mast and antennae. We anticipate topographic, aerodynamic and aeroelastic
wind tunnel testing will be required to confirm:
a) The effect of local topography on design wind speeds,
b) that the design of the fabric does prevent the generation of oscillation-causing wind
vortices,
c) the absence of galloping instability, and
d) the forces that the structure is subjected to
Public and fire observation decks.
While it would be possible to cantilever these floors outwards from the central mast, and
possibly restrain them using the guy cables, it was felt simpler and easier to support the
outside edges of the decks with inclined steel columns that spring from the roof of the lower
level accommodation. The floors consist of 150mm thick concrete slabs supported by 350mm
deep steel beams. Whether the floor slabs are precast or cast in-situ will be determined by
consideration of the practicalities, benefits, costs and risks of both approaches.
Lower accommodation
The two storey lower accommodation will be constructed of reinforced concrete slabs,
beams, columns and shear walls. The significant self-weight of the lower accommodation
helps to resist the overturning forces cause by wind and seismic loading on the mast,
antennae and fabric.
Foundations
The briefing documents have confirmed that:
 Ground conditions within the area are typically (from top to bottom and with various
thicknesses of soil layers) top vegetated soil, high plasticity fat sandy clay, low-tomedium strength sandstone, and stiff low plasticity sandy clay.
 Allowable bearing strength of the soil is proposed as 0.5MPa (5kgf/cm2) or larger.
 A local site class of Z2 is proposed. Spectrum characteristic (corner) periods are
TA=0.15s, TB=0.40s. Also, a soil group of C is proposed. Fundamental period of soil is
given as To=0.34s.
 Closest fault line to the site is 23kms away. A M=7.2 ~ 7.5 magnitude earthquake is
expected on these fault lines.
 There is no liquefaction risk in the area.
 No ground stability problem is expected in the area.
 No ground water level is observed during the soil investigation.
The total weight to be carried divided by the footprint of the lower level accommodation is
comfortably less than the anticipated allowable bearing strength of the soil. That, and the
absence of liquefaction, ground instability or a high water table in the ground, all point to
simple shallow foundations. It is anticipated that a grillage of reinforced concrete strip
footings will constructed to transmit vertical and horizontal forces into the ground. These will
support seismic base isolators which will in turn support the lowest level of the lower level
accommodation.
Base isolation
The following table briefly compares the different strategies that may be employed for
providing adequate seismic resilience.
It can be seen that base isolation has the potential to reduce the seismic load on the structure
more than any other approach, and to minimise damage to structural and non-structural
elements. Care will be needed in detailing interfaces where movements can occur. Uplift is a
potential problem but experience on other projects shows that this can be dealt with.
Preliminary calculations suggest that, thanks to the weight of the lower accommodation,
uplift should not occur.
Seismic
Possibl Damage to Damage
Wind
Ease of Detailing
Resilience
e base
Structure
to NonResponse
Strategy
shear
Structure
Strengthen
100%
Minimal
Plenty
Good
Movement throughout structure
Isolate
35%
Minimal
Minimal
Damping
55%
Some
Some
Needs
attention
Very good
Tricky at interface, easier
elsewhere potential uplift problem
Tricky at façade near dampers
Rocking /
Damping
Active /
semi-active
TMD
60%
Some
Some
Good
Tricky at base and in façade
45%
Some
Some
Very good
Easiest detailing, but potentially
expensive system. Questions of
reliability
Broadcast Technology Report
The Brief
From the spaces and functions section of the brief and our research of recent developments in
broadcasting in Turkey, we can establish that the key requirements are to: Provide a common antenna and transmitter system to consolidate several existing
masts and comply with the 2011 laws set out by the Radio & Television Supreme
Council (RTüK). This will provide a number of benefits including:o a reduction of interference and compliance with International frequency
allocation treaties;
o provide a better and more consistent viewing experience for viewers and
listeners through common ownership and single point of responsibility;
o potentially reduce total energy consumption through the more efficient use of
power.
 Provide N+1 redundancy for 7 UHF TV multiplexes, 1 VHF TV multiplex and 50 FM
analogue radio channels on a single tower with safety distances, maintenance
platforms and a viewing platform.
 Allow safe access to a public viewing platform on the mast.
1. Broadcast Principles
The broadcast of digital radio and TV signals is concerned with providing coverage for all
required services, with an acceptable range of signal strength and quality to the target area.
This area is usually defined as part of a master plan for each country taking into account
existing and future anticipated population densities. At the same time it is important to avoid
interference to neighbouring areas which could include other countries. This function is
influenced by a number of variables including: The height, gain and directionality of each antenna or array,
 The power input to each antenna,
 The loss within the communications infrastructure (feeders, combiners, filters),
 The terrain path loss.
While the provision of broadcast infrastructure is generally a well-established process, there
are a number of challenges with this project in particular: The maximum total antenna height limitation set out in the planning consent, given
the amount of equipment and ancillary spaces required on the mast;
 The undefined coverage area required for each service;
 The need to accommodate 50 analogue FM radio channels into 5 “master” antennae
and the consequent space for combiners and dummy loads that this approach entails in
the Transmitter Room;
 The radiation hazard to users of the viewing platform.
2. Technological Response
Coverage assumption
While all services will need to cover the immediate town of Çanakkale, it is assumed that
some TV and radio services will need to reach the outlying smaller towns making a
maximum coverage of up to 70Km from the transmitter site. This is a worst case scenario and
if it is subsequently confirmed that less coverage is required, then this will benefit the design.
Indeed it will be necessary to restrict the power output for some antennae if there are other or
planned transmission sites within this distance.
Another assumption we have made, again as a worst case, is that the coverage will the same
distance all around the site (Omni-directional). We know from the terrain sections that this is
unlikely in practice since in some directions there is no apparent population and in other
directions there is obstruction from higher ground. Controlling coverage in particular
directions will again benefit the design as well as operating costs.
Stack layout
We have arranged the stack in accordance with best practice meaning the smallest UHF
DVB-T antennae at the top followed by the VHF DVB-T in the middle and five VHF radio
arrays taking up the bulk of the space below. This approach will also help with the structural
requirements, with the larger, heavier units being lower down the mast. The lower antennas
will have progressively smaller coverage and can consequently be fed with less power. The
50 radio stations will therefore need to be grouped according to their coverage requirements
for example with the community based channels at the bottom and national/regional ones
further up. Finally a zone has been allowed for the point to point microwave links required
for backhaul connectivity.
One of the unusual features of the project is the public viewing platform on the mast. This
presents a potential radiation hazard particularly at the frequencies used in FM radio and the
distances involved. The safety limits for such radiation exposure are set out in the ICNIRP
guidelines and define lower limits for public exposure than for occupational exposure.
Control of Exposure
Our approach to controlling this exposure is to maximise the distance between the antennae
and the public areas, control the power level progressively such that the lowest antennae
nearest the public platform have the lowest power and limit power immediately below the
mast in so far as possible within the constraints of available products. Our calculations
indicate that power densities and field strength can be comfortably contained within the
guidelines set out. In addition we would propose to provide some screening using the Faraday
principle between the antennae and the viewing platform which will further attenuate the
field strength in this direction Finally we would advocate an operational policy that limits the
amount of time people spend on the platform which is likely to be needed anyhow due to the
limited space in relation to the main public space.
Equipment & Monitoring room space
The main Equipment and Monitoring Room space will accommodate all of the TV and Radio
transmitters, combiners, filters and dummy loads. In addition a media wall and control desk
will be provide for engineers to monitor outputs and take corrective action where required.
The later will also be visible from the public area above making an interesting viewpoint for
visitors.
3. Third Party Opportunity
Although not mentioned in the brief, we can see a potential opportunity for revenue
generation for the provision or leasing of space on the mast to 3rd party operators such as
Telco’s. We have thus made a separate space allowance both in a zone on the tower and on
the ground for the associated technical equipment and feeder space between the ground and
the tower.
4. Radio Frequency Properties of Kedlar (PVF)
The Tower is to be covered by Kedlar. Our initial investigations suggest that this will not
impact the radio frequency propagation characteristics of the antennae nor will the RF energy
degrade the material properties over the longer term.
5. Exhibit Technology
As well as the Mediatheque space in the brief, we propose a media wall is used in the main
exhibition space to provide a composite “dashboard” view of the transmitter outputs in a
visually engaging form which would include simplified bar-graphs and oscilloscope traces.
This could be further supplemented by a number of interactive displays that allow visitors to
engage with the technology at their own pace and from a safe distance. Metrics such as the
temperature, pressure and wind speed at the top of the mast and power consumption for the
site could add further interest. A couple of webcams could also relay images to the exhibition
space as well as potentially on- line.
6. Budget for Broadcasting Systems
We believe that the 3m TL estimate is sufficient for the components and installation of the
broadcasting systems based on current assumptions.