Below podium

Most of the podium has garages or commercial premises (such as the Virgin Gym) underneath. For those areas to be usable, it’s important that the columns supporting the podium above are not too close together.

As a general rule, in the South Barbican the columns are spaced 35 feet apart. The roof was then formed of a square grid of reinforced concrete ribs with a reinforced concrete slab over the top. This structure was necessary because the height of the garage floors did not allow for the use of deep beams.

In the North Barbican column, the column spacing is about 23 feet apart and a more conventional flat slab structure was adopted.

These slabs can normally sustain considerable changes in temperature without cracking, but due to the heavy loads and large spans on the Barbican estate, the upper podium slab was broken up into areas not exceeding 150 square feet and fitted with expansion joints which separate the slabs structurally. These expansion joints or “structural discontinuities” were made watertight by the use of flexible water bars.

Where the podium covered Beech Street, it was necessary to modify the basic structure to deal with the increased spans.