Structure of buildings in the Barbican Estate

“Their ideas are expressed in cyclopean reinforced concrete forms, massive far beyond utility (and indeed the flats were never meant to be cheap).”

The Buildings of England” Nikolaus Pevsner and Simon Bradley

Work on the buildings began in 1963. The Barbican estate, as eventually built, employed concrete in a much more monumental way than was envisaged in the comparatively delicate designs in the 1959 Report. This was made possible by using in situ reinforced concrete as the method of construction. The opportunity was provided by the engineers’ adoption of deep beams spanning between wide-spaced cross-walls, which Chamberlin Powell & Bon exploited as a feature, particularly in the more exaggerated forms of the external balconies.

The structure of the Barbican estate basically consists of concrete buildings, on top of massive columns, standing on bored pile foundations. The buildings are constructed of reinforced concrete for the most part, but there are some areas where pre-stressed concrete was needed.

Many of the terrace buildings of the Barbican estate are carried on columns 1.2 meters in diameter. The idea was to open up the space around buildings and create continuity between different parts of the layout. The desired effect was that people would always see a large vista around them, which would avoid any feeling of oppressive enclosure by large buildings.

The terrace buildings have a simple structure of reinforced-concrete load-bearing cross-walls and floor slabs. The use of cross-walls simplified the construction work. A cross-wall forms an internal flat wall which needed painting but not plastering which was a further saving in time and cost. The junctions between walls and slabs provide the stiffness to ensure each block has longitudinal stability.

The tower blocks have an entirely different form of structure. Each block was formed of pre-cast structural reinforced concrete units which were designed to form framework round the outside face of the buildings. This was the main structure; internal walls were to provide further secondary stability and some load bearing capacity.

The concrete throughout the estate was made with Pen Lee crushed granite, which Nikolaus Pevsner in “The Buildings of England” described as “used in tough masculine forms on a mighty scale”. Two grades of structural concrete were used with 28-day cube strengths of 34 N/mm2 and 42 N/mm2. For the most part, all batching and mixing of concrete was carried out on site.

All the walls and floors were made on site. Carpenters had to create frames like open boxes using three-quarter inch plywood to the size of the required wall or floor. Then the concrete was poured in and left to set. This usually took 28 days. The walls would also have metal backs bolted on to them. Once the concrete in the shutters was dry the shutters would be lifted up by  crane. Shutters were 20 feet long or more. They were dropped in place and would then be bolted to other shutters and/or structural framework.

The concrete walls were thicker at the bottom of a building where they would carry most weight. There the slabs might be 2 feet or 18 inches deep. Higher up the building, with less weight to carry, the walls might be reduced to 12 inch slabs.

The walls had to be pick hammered to achieve the consistent surface appearance of all the buildings. The work couldn’t be done until the concrete was absolutely dry, so pick hammering took place once the had been lifted into place.