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Structures Restructured | Cape Town grain silos

776 3 hr zeitzmocaa heatherwickstudio credit iwan baan view of zeitz mocaa in silo square

Proving what can be done to reuse existing assets, a disused grain silo has been reborn as a museum in Cape Town, South Africa.

Back in 1920s South Africa, Cape Town’s 57m high grain silo was the tallest building in sub Saharan Africa. Over the decades it became an icon of the city’s skyline. The complex fell out of use in 1990 and was left derelict but was still an important backdrop to Cape Town’s busy V&A Waterfront with its blend of commercial and, residential developments, cruise terminal, and entertainment all in a modern day working harbour.

Thanks to some extremely inventive reuse and renew thinking, the grain silo will now add to the mix as it has been reborn as the new Zeitz Museum of Contemporary Art Africa and Silo Hotel. It includes a stunning gallery atrium scooped out of the tightly packed silo tubes to form the building’s heart.

776 9  hr zeitzmocaa heatherwickstudio credit iwan baan atrium at night

776 9 hr zeitzmocaa heatherwickstudio credit iwan baan atrium at night

Source: Heatherwick Studio

The silo structures have been sliced to create internal space

The team behind the reuse and renew project for client Victoria & Alfred Waterfront were Heatherwick Studio and Arup, working with local structural engineer Sutherland. The £30M, 9,500m2, not for profit public museum project is a partnership between the V&A Waterfront and German entrepreneur Jochen Zeitz. Included in the development is over 6,000m2 of exhibition space in 80 galleries, a rooftop sculpture garden, storage, conservation areas, a bookshop, restaurant, bar and reading rooms.

“On hearing of the architectural vision for the buildings, we visited the site and studied the archive drawings and photographs,” says Arup associate director Francis Archer.

“As the existing buildings were near 100% structure, both concrete and steelwork, we developed some basic structural principals with Heatherwick Studio to apply across the project. These can be summarised as ‘re-use or strengthen where possible’, but also unashamedly ‘demolish and build’ bold new sympathetic structures to enable the vision of a functioning gallery and hotel.”

The storage annex matrix of 42, 30m high tubular silos was carved away  internally  

Though the concrete building looks like a single structure, it has two parts: a grading tower and a storage annex of  42 cellular silos. A concept was developed to carve out the atrium at the museum’s heart, to provide access to the gallery floors organised around it and tie these two structures together.

“The grading tower was a multi-storey steel structure that was robust and generally in good condition. New cores were needed both for escape stair, lifts and risers but also for stability as the original perimeter concrete wall panels were to be removed to open up the building at low and high levels,” Archer explains.

Structural work

Original filler joint floors were strengthened with a reinforced topping slab, and new reinforced concrete slab floors added within the lower silos. Three primary columns were cut away at lower levels, as part of the atrium cut out at the interface with the adjacent tubular silos annex. The column loads were transferred through major reinforced corbels into the new cores.

“ The storage annex matrix of 42, 30m high tubular silos was carved away  internally to create a multi-storey gallery to the east, as well as the large atrium cut out to the west,” Archer explains.

“The remaining silo walls were no longer structurally integral but needed to be held in their original form. The idea of resleeving the cylindrical forms with a layer of reinforced concrete was developed, thus creating an entirely new building structure in and around the old and able to hold the old in place.”

Cut out silo sections

The huge cut outs were designed to look like scaled up grains of corn. To create the 27m high shapes, thousands of co-ordinates were pinpointed within each silo’s tube and mapped out physically with nails to guide the formwork. The brittle, 170mm thick concrete tubes were then lined with partial inner sleeves of reinforced concrete to the exact shape of the new atrium.

Silo location

Silo location

The new concrete sleeves created a stable composite structure 420mm thick, and provided a cutting guide for removing portions of the old silos which were pared back to reveal the curved geometries of the 4,600m3 atrium. The cut edges were polished to give a mirrored finish that contrasts with the structure’s rough concrete aggregate.

Each of the carved tubes was capped with a 6m diameter panel of laminated glass that brings daylight into the atrium. The remaining internal tubes were removed to make room for the gallery spaces.

External glazing

The greatest change to the building’s external structure was the pillowed glazing panels that are inserted into the existing geometry of the grain elevators’ upper floors. The glazing has turned the tower into an illuminated beacon creating irregular, sparkling patterns and acting as a lantern for the harbour and the city beyond.

 “Financial feasibility, and construction sequence were key to this ambitious scheme and we worked closely with the contractor WBHO, quantity surveyor MLC and project manager Mace, as well as Cape Town-based Sutherland Engineers to whom we passed on the scheme design for detailed development and construction,” Archer reports.

“The idea of turning a giant, disused concrete grain silo into a new kind of public space was weird and compelling from the beginning,” says Studio Heatherwick founder Thomas Heatherwick.

“The technical challenge was to carve out spaces and galleries from the 10 storey honeycomb without completely destroying the authenticity of the original building.

“The result was a design and construction process that was as much about inventing new forms of surveying, structural support and sculpting as it was about normal construction techniques.”




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