Tower Construction

construction / engineering

Piling work started in November 2001. 84 large cast in-situ piles create the foundations to the Tower. The longest pile has been drilled approximately 50m into the seabed – the equivalent of Nelson’s Column. The total length of all the piles is 3.3km (2.05miles), equivalent to the distance from the Spinnaker Tower to Fratton Park.

Starting in Jan 2002, a pre-cast raft was constructed in order to build the main concrete raft. The raft is 2.5 - 3 metres deep and is supported on piles, with several layers of reinforcement cast inside the mass concrete, creating the main foundations of the tower shafts.

From 10 March to 27 June 2003, the concrete A-frame of the Tower was constructed using a technique called slip-forming, where concrete is poured continuously into moulds used to create the hexagonal shafts of the tower. Progress was made quickly as concrete was poured at a rate of 25mm in 20 minutes (2.7metres a day). The structural bows of the Tower were constructed using approximately 1100 tonnes of structural steel – equivalent to 11 blue whales. The bows were fabricated and erected into position in various sections. The largest section being the “cruciform” weighs approximately 95 tonnes. The steel sections were fabricated by Butterley in Derby, the same company that produced the deck beams for HMS Warrior back in 1850.

The first stage of lifting the steel work started in March 2004 and was to erect a system of trestle supports at ground level, to enable the connection of the various sections forming the lower bows.
This was followed by a lifting process, which was achieved via a proprietary process, known as strand-jacking. This is a system using hydraulic jacks and high tensile wire ropes located at strategic points.
To erect the upper bows, spacers and ribs, required the help of a tower crane, each section being lifted into place one by one. The tower crane used was one of the tallest “free standing” cranes of its type in Europe.
While work was progressing on the steelwork, other areas of work included the construction of the internal lift, which was underway inside one of the legs of the concrete shafts. This lift carries 26 passengers at 4m/sec, reaching view deck 2 in approximately 30 seconds. The panoramic glass lift has been manufactured in Italy by a company who specialise in lifts for unusual inclines, such as Alps. This lift can carry 16 passengers at approximately 1.6m/sec, reaching view deck 1 in approximately 70 seconds.

Structural glazing for the Spinnaker Tower has been produced by a Winchester company, using a highly specialised structural glazing system. The glass becomes its own support with the assistance of glass fins and stainless steel posts. The installation of the 27m tall, 14 tonne spire took place in January 2005, bringing the tower to its finished height of 170m.

Internal fit work took place from this period to opening to turn the tower from a construction site into a visitor attraction. This included the installation of the entire visitor pods, café/bar and ticketing area.

The Tower opened to the public in October 2005, and has become an instant success, attracting nearly one million visitors in under two years.