Construction World March 2017

“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”.

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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CONSTRUCTION WORLD MARCH 2017