Construction World December 2016

Joint Winner

Professional Services C PwC TOWER

The horizon of Midrand, north of Johannesburg, is set to change forever with the construction of the new high-rise head office for Pricewater- houseCoopers (PwC). The R1,5-billion project will be a focal point in the up and coming Waterfall City development and comprises 45 000 m² of modern offices, designed to house 3 500 PwC employees in an efficient and optimally designed workplace. It is set to become a structure of iconic proportion due to its distinctive twisted form designed by LYT Architecture for Attacq Waterfall Investment Company and their developer Atterbury, and realised through close collaboration with Arup. The structure is a concrete frame with post-tensioned (PT) floor plates and each floor of the 28-storey office tower rotates 1,2 degrees relative to the floor below. The core of the building was constructed using a method called slip forming, where the concrete is poured continuously within the steel shutters, which moved up at a pace of 2,5 m a day. The Arup façade engineers worked closely with the façade contractors Geustyn & Horak on a new suite of extrusions specifically for this project, which is the first curtain wall in South Africa with twisted unitised panels. Parametric modelling can be described as modelling a structure or object in an n-dimensional space, where certain chosen parameters of the structure are adjustable. The biggest structural challenge was that the spiralling form of the tower causes the gravity loads to create naturally a clockwise torsional load on the building.

The PwC façade is concave and twisting, and knowing the history of high profile cases with problems caused by concentrated solar reflections from buildings (notably those at 20 Fenchurch Street in London – the ‘Walkie- Talkie’ – where plastic fittings on a Jaguar on the street melted in 2013), the Arup team identified this as a risk and knew this was something that would need careful study for the tower. At the time of design, no software existed for calculating the intensities of solar reflections. Arup therefore scripted its own calculation in parametric software. Using this script, it 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 façade, randomly scattering façade panels and making spandrels non-reflective. In the end, it was decided that the best solution was to use a less reflective glass in the spandrels that was further enhanced by acid etching. Landscape shading addressed any remaining concentrations over limit. 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. As of 15 September 2016, there has been only one hour of lost time due to injury over 2 260 000 total man hours on this project.

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Project information • Company entering: Arup • Client: Attacq Waterfall Investment Company

• Start date: October 2014 • End date: October 2017 • Main contractor: WBHO • Architect: LYT Architecture

• Project manager: LYT Architecture • Quantity surveyor: Brian Heineberg and Associates

• Consulting engineer: Arup • Steel contractor: Amsteele • Façade contractor: Geustyn & Horak • Mechanical engineer: WSP

Construction WORLD

DECEMBER • 2016