BT Tower visit of the revolving floor

History:

The BT Tower was designed by the Ministry of Public Works under the direction of Chief Architect Eric Bedford. The senior architect involved in the project was Mr G R Yeats and the main contractors were Peter Lind & Co Ltd.

Construction began in April 1961 and was completed some four years later, opening for operations on 8th October 1965 by the then Prime Minister Harold Wilson.

Construction problems:

As construction began a borehole survey of the site revealed a tricky problem. There was hard chalk – suitable for supporting the foundations – beneath the blue London clay, but it was 53 metres down and therefore an alternative way of supporting the 13,000 tonne structure was needed.

An Italian firm came to the rescue, laying a concrete raft on the clay, some eight metres below ground level. The raft measures around 27 metres square, is one metre thick and reinforced with six layers of steel cables. On it sits a seven metre tall reinforced concrete pyramid with a flat top. The raft and pyramid together provide the foundations and, on top of them, a hollow reinforced concrete shaft runs from near enough ground level, right up through the centre of the tower. This is the backbone of the whole structure which, together with a collar connecting it to the adjacent four-storey building, gives the Tower its stability.

A climbing crane was used to build the Tower; this was later dismantled and lowered from the top by its own winch.

As with other tall buildings, the structure expands and contracts as the temperature changes. This means that in winter the Tower can be as much as 23cm shorter than it is in the summer.

The revolving floor:

The revolving floor had to be prefabricated and hoisted up in sections, there is a three millimetre clearance between the revolving and stationary sections of the floor and yes, it still revolves today. Two high-speed lifts transport visitors to the upper levels of the Tower, taking just over 30 seconds to reach the top.