Construction World December 2015

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Building Contractors

The Towers

storey building linking the two towers. A planned upgrade of the complex to an A-grade office building incorporated wrap- ping the envelope in high performance architectural glazing. It also involved adding an additional 1 500 parking bays in the form of a 13 storey parking structure between the two towers, as well as upgrading of the public square. Construction commenced in April 2013, with the parking structure columns being constructed in the current basements. The existing foundation of the seven storeys was insufficient to cope with the loading of the proposed 13 storey parking garage. New foundations were required for the basement, which continued to operate in the interim as a three level parking garage for the tenants. After construction of the founda- tions for the new columns, a letterbox was constructed in the existing slab above these to facilitate the casting of the concrete for the column. Once the first column on the lower basement level was cast, the slab above was back propped and a bigger aper- ture was cut to extend the column through the slab. Concurrently with this operation the existing four storey link building, situated between the two towers and on top of the old parking area where the columns were being constructed, was being demolished. The construction programme was carefully coordinated to ensure that the construction progressing from the basement level upwards would simultaneously meet with the demolition of the four storey link building on the ground floor. Once this was

Careful planning and management of façade cladding activities allowed Murray & Roberts Western Cape to gain 38 days on the construction programme for Redefine Properties’ The Towers project in Cape Town’s Central Busi- ness District. An emphasis on innovation, teamwork and safety characterised this landmark project, which was completed in August 2015. Originally built in the 1970s, The Towers, previously known as The Standard Bank Building, consists of two towers, a 13 and a 23 storey building complex, with a four

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accomplished, the construction of the 14 storey garage began. One of the interesting challenges encountered on the project was main- taining a column-free space in the existing ground floor public square, with the top 10 levels of the parking structure cantilevering 13 metres over this square for a distance of 50 metres. This was achieved with the construction of a 55 metre span by 25 metre high A-frame megatruss. The truss is designed to span 50 metres, carrying nine suspended floors by transfer- ring the gravity load to the L-shaped shear walls at the ends. What is especially noteworthy is the fact that an entirely separate, temporary concrete structure was built, complete with five piles, to support the A-frame until the full frame was completed, whereafter the temporary frame was demolished. This was required due to the large magnitude of the temporary loads, which would overload any conventional back-propping system. Once the A-frame was completed, the tension ties and hangers were prestressed to between 5 000 and 14 000 kN and the bearing on the temporary columns was released through a phased down- ward-jacking process, using 8 000 kN flat- jacks on top of the temporary columns.

Project information • Company entering: Murray & Roberts Western Cape • Project start date: 20 June 2013 • Project end date: 30 August 2015 • Client: Redefine • Main contractor: Murray & Roberts Western Cape • Architect: Smuts & Boyes • Principal agent: BFH de Jager Project Managers • Quantity surveyor: LDM Quantity Surveyors • Consulting engineer: Aurecon SA • Subcontractor (façades): World of Windows • Project value: R370-million (excluding VAT)

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CONSTRUCTION WORLD DECEMBER 2015

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