The making of the PwC Tower…
… with a twist of Arup
North of Johannesburg the Midrand skyline is set to change forever with the construction of the breathtaking PwC Tower in the Waterfall City development project.
The building is poised to become a structure of iconic proportion due to its distinctive twisted form designed by LYT Architects for Attacq Waterfall Investment Company and their developer Atterbury and realised through close collaboration with Arup – one of South Africa’s leading design engineering consultancies.
To achieve the building’s twist, each floor of the 28-storey office tower rotates 1.2 degrees relative to the floor below. This posed a variety of design challenges for both the structure and façade, many of which Arup was able to solve creatively and efficiently using parametric modelling.
“We needed to ensure our design solutions met the architect’s intent and that a creative concept could be successfully applied,” Richard Lawson, buildings associate at Arup says. “At Arup we are fortunate to be able to share cutting edge research and technology within our global network. It enables us to tap into the latest scientific knowledge and creative thought, which when combined with the utilisation of software, allows us to push the boundaries of design. Our advanced parametric modelling software and systems enables us to explore many options in our search to establish the optimal solution for complex building designs such as the PwC Tower project.”
“A further beneficial aspect to parametric modelling is the way it feeds into other software, particularly our Building Information Modelling (BIM). Arup uses BIM as our default method for producing and managing design work.
Arup façade engineer Rudolf le Roux describes parametric modelling as “modelling a structure or object in an n-dimensional space, where certain chosen parameters of the structure are adjustable”. In other words it makes it possible to explore the impact of any of the input parameters on the design and cost of a structure.
“The biggest structural challenge was that the twist causes the gravity loads to naturally create a clockwise torsional load on the building,” explains Lawson. “The obvious solution to this would have been a very thick core wall, but because we were able to quickly asses a number of different structural geometries, we were able to optimise the solution. Our 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; therefore we could use a 450 mm thick wall which is not much thicker than a typical straight tower of that height would have needed.”
Le Roux continues, “We also utilised parametric modelling for the design of the façade for the PwC building. Various solutions were on the drawing board 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 made possible through parametric modelling.
“What we really enjoyed was that we could 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 makes collaboration easy, and results in far less exchange of correspondence back and forth,” explains le Roux.
Guy Steenkamp, Director of LYT Architecture agrees, “The team at Arup brings international experience to the project, although they are all local professionals. The kind of systems and thinking that they were able to apply to the design really made that building possible, so it’s as much their design as it is ours.”
Beyond the structure
Parametric modelling was even used in some more unusual aspects of the building’s design. Given that the PwC façade is concave and twisting, and knowing the history of high profile cases of problems caused by concentrated solar reflections from buildings – notably those at 20 Fenchurch Street in London, known as “the Walkie-Talkie” (where the focused glare of the sun from the concave surface of the building caused damage to nearby shops and vehicles) – the Arup team knew that this was something that would need careful study for the tower.
“At the time of design no software existed for the purpose of calculating the intensities of solar reflections,” said le Roux. “Since the exact geometry of the façade had already been created in the parametric software, we used it to calculate and add up reflections from the façade. We could also test the effect of different proposed counter measures by including additional parameters such as glass reflectance and installation tolerances. With this knowledge, we were able to provide feasible and practical solutions to mitigate the impact of the solar reflections.”
All projects can benefit
Lawson adds, “Many factors went into the parametric modelling equation for the PwC Tower to come to the final optimised solution. Our use of parametric modelling software on a project of this scale is unique within South Africa, and our clients, as well as ourselves, are reaping benefits from the optimised holistic design on projects where we are collaborating.
“The beauty of taking a parametric design approach is both in time and cost efficiencies and a better integrated and well considered design, with all architectural and construction factors in sync.
Arup is the creative force at the heart of many of the world’s most prominent projects in the built environment and across industry. From 92 offices in 40 countries our 12,000 planners, designers, engineers and consultants deliver innovative projects across the world with creativity and passion.