Construction World June 2019

PROJECTS & CONTRACTS

CREATING A LANDMARK At 55 floors the Leonardo in Sandton will officially be the tallest building in Africa. The much anticipated final concrete pour on the Leonardo’s sky deck has just been completed, bringing to an end the speculation as to its final height.

T his speculation was largely due to the strategy adopted to have a flexible approach to the height of the building: it was dependent on sales. The original contract was for 32 floors with a first phase including parking and podium to the 5 th floor, back in November of 2015. Over time this increased to 33, 40, 42, 47 and finally 55 floors, the maximum height in terms of its rights. Sales have gone well and only 16 units remain unsold. According to Patrick McInerney, CEO and Director of Co-Arc International Architects, the architect’s design of the building had to anticipate each of these potential heights and an adaptable way had to be found to deal with the attendant structural and servicing issues. Detailing the building for a variety of potential heights created a challenge for the professionals. This was compounded by the design and construction of the building that had to take account existing foundations from a previously failed project by other developers. In contrast to the environmentally inefficient east-west facing orientation of the original development, Co-Arc was able to design a very slim and efficient central core for a rectangular building facing north- south. This worked with a structural grid designed to avoid the existing footings and incorporate the massive concrete base, already on site. “The architecture of the building was dictated by founding conditions, but

presented a number of opportunities for how goods and people could be distributed and move horizontally and vertically through the building,” says McInerney. Two escalators and 15 lifts in 12 lift shafts give access to seven reception areas distributed through the building. This allows ease of access and communication to the different functions within. These include residential appartments, offices, retail, restaurants, gym, health spa, crèche, pharmacy, flexible conference venue and a hotel. Eight separate sets of stairs provide fire escape routes and circulation. The majority of these and the complex services required are contained in the structural core. The core The core is the main stabilising element for the structure and is sufficiently robust to deal with the extremely remote possibility of catastrophic failure affecting the building. In such an event, external column loads are transferred in giant beams back to the main core at intervals of 11 floors. According to the architects, these interruptions to the façade provided opportunities for service plant rooms to be evenly accommodated throughout the height of the building at intervals which suited hydraulics for the piped services, the distribution of air and refrigerant for air-conditioning, smoke extraction, fire pressurisation, as well as data cable lengths. “The service floors with their deep

outrigger beams become articulating elements in the design, making legible the structural and organisational logic of the building in its profile and façades. The efficiency of a coordinated approach to design is evident in that a total of only 13 m 2 per floor is used for all of the service shafts in the building, most of which are accommodated in the core. “The thin, long and narrow core makes it ideal to use a hydraulic shuttering system,” says McInerney. The core was built using the Peri hydraulic formwork system, which according to Francois Pienaar of Aveng (the main contractor), was only the second time in South Africa where this system has been used. It enabled continuous workflow throughout the project with no formwork or scaffolding in the way to allow slabs to be decked and constructed continuously with no interruptions. Following approximately four floors behind the core, the column free construction of slabs in the tower levels were cast. These were staged to allow for the next level to be decked within two days after pouring slabs. Defying gravity Concrete defied gravity by being pumped over 200 m into the air. This required a fluid mix of concrete and for the pipeline to be tightly secured with minimal movement. One of the main riser ducts in the core was used to secure the pipe. This ensured that

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CONSTRUCTION WORLD JUNE 2019