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CONSTRUCTION WORLD
MARCH
2017
solution to this would have been a very thick core wall – initial
calculations showed that with this scheme a 2 m thick core wall
would have been required to resist this torsion. A solution was
sought in which the structural columns could reduce or counter
this torsional load. Due to Arup’s advanced parametric modelling
software and systems, a number of different structural geometries
were quickly assessed and an optimised solution found.”
The final scheme incorporated structural columns on the façade
of the building that slope in a counter clockwise direction around
the core, balancing the gravity loads on the corner columns and
reducing the torsion on the core of the tower. This meant that the
stresses on the core wall decreased by a factor of four and a
450 mm thick wall could be used – which is not much thicker than a
typical straight tower of that height would need.
“One of the early questions faced by the design team was the
type of façade to be fitted to the concave twisting surfaces of the
building, so we also used parametric modelling for the design of
the façade,” explains Rudolf le Roux, engineer in Arup’s Façades
team. “Various solutions were considered at the conceptual stage
with factors such as glass utilisation, aesthetic integration with the
structure and integration of blinds with a sloping, slanting façade.
Building a concave, twisted façade out of straight aluminium
profiles and flat glass was a challenge overcome through parametric
modelling. As part of the process, we were able to sit down with
the architect and make real-time adjustments to things like the
column spacing and angles that they could see instantly in 3D.
It made collaboration easy, and resulted in far less exchange of
correspondence back and forth.”
Environmental considerations
The building is designed to be a Leadership in Energy and
Environmental Design (LEED) Silver Green building and the
environmental impact due to construction activity is strictly
monitored. The building itself will comply with all latest sustainable
and energy-efficient requirements in terms of the air-conditioning
system, the light fittings and the selection of glass used in the
façade. The following sustainable design features were implemented
within the Arup scope:
Structure
• The concrete for the superstructure is specified to reduce the
absolute quantity of Portland cement by an average of 60%
for in-situ concrete, 40% for precast concrete and 30% for
stressed concrete.
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“Because tall buildings of this scale are no longer
the norm in South Africa, the team had to consider
appropriate current methodologies and technologies
throughout design. We believe this project highlights
one of Arup’s founding principles – that of holistic
design. The PwC tower is being made possible through
industry collaboration and the embracing of technology
to facilitate that collaboration”.