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CONSTRUCTION WORLD
MARCH
2017
36
PROJECT PROFILE
• Where possible 60% of all reinforcing steel and steel products
should have a high-recycled content.
• The building will have post tensioned concrete slabs, as opposed
to conventionally reinforced concrete slabs. Post tensioned slabs
are substantially thinner and have less reinforcing steel in them
than conventional RC slabs. This not only reduces the material
used in the slabs but also reduces the size of the columns,
foundations and the concrete core walls. This will reduce the
amount of concrete and reinforcing steel used in the project by
more than 10%.
• The same principle applies in reducing the size of the core wall
through parametric optimisation.
Façade
Performance glass is used to minimise the mechanical plant
requirements and reduce operational costs.
Infrastructure and wet services
• Rainwater harvesting is future enabled. Rainwater will be drained
from the building roof using a Pluvia type system. The downpipes
will run vertically in the core and connect in a network in the
basement levels to storage tanks that could be filtered and used to
supplement the supply of water for flushing of toilets and urinals
in future.
• A sump in the lowest basement level collects ground water
seepage through the retaining walls and is pumped out by means
of a submersible type pump to irrigate the PwC gardens and the
neighbouring park. This water would have otherwise connected
directly to the storm water system and been lost.
• All excavated material has been locally reused on the rest of the
Waterfall City site.
Quantifiable time, cost and quality
Optimisation and collaboration
The tower has complex geometry and various options have been
reviewed, with the help of parametric modelling, to identify the most
efficient way of supporting the structure that complies with the
architectural intent. “Close alignment with the façade design has
allowed a seemingly difficult form to be achieved with a reasonable
degree of repetition and coordinated detailing. Buildability and
maintainability have also influenced the structural and façade
design,” adds le Roux.
Construction programme reduction
Programme reduction was taken into account when completing the
design of the project. To reduce lead time before breaking ground
on site, Arup issued earthworks as a separate package ahead
of the rest of the building. For a tall building the programme is
governed by the floor to floor cycle time. Slip forming the core adds
an early activity to the programme but then allows each floor to
be completed more quickly, saving time overall. The use of bonded
PT slabs also allowed the floor cycle time to be reduced without
compromising the future flexibility of the building.
Façade
The curtain wall is constructed using the unitised principle in which
complete glazed panels are made in a factory and then installed
onto pre-set brackets on the building. This means that:
• No scaffolding is required, which would have been very costly for
the almost 100 m height and 20 m overhang of the top floor over
the ground floor.
• Curtain wall installation can proceed before all concrete floors
are cast
• Quality is better controlled in a factory than on site.
• Panels can be installed quickly, typically 20-30 panels per day.
• Panels are watertight as soon as they are interlocked in position,
allowing following trades to commence immediately.
Risk management
Concentrated solar reflections
Le Roux comments: “The PwC façade is concave and twisting.
Considering several high profile cases beset with concentrated solar
reflection problems (notably those at 20 Fenchurch Street in London
– the ‘Walkie-Talkie’ – where plastic fittings on a Jaguar on the
street melted in 2013), concentrated solar reflections were identified
as a risk for the tower and needed careful study. At the time of
design, no general analytical software existed for calculating the
intensities of solar reflections. A purpose-built script was developed
for this analysis, with the results benchmarked against other Arup
studies globally.”
Using this script, Arup was able to calculate the magnitude of the
solar concentrations in the open areas surrounding the tower and
provide feasible and practical solutions to mitigate the impact of
the solar reflections. Solutions considered were sunshades on the
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