HISTORY Emirates Spinnaker Tower was built as part of the centrepiece of the Renaissance of Portsmouth Harbour Project and has become Portsmouth’s most prominent landmark. Visible beyond 23 miles away; it dramatically overlooks the Portsmouth harbour, Gunwharf Quays, Portsmouth Historic Dockyard, City centre and all of Portsmouth and its neighbouring towns and suburbs. A prestigious Millennium Project, the proposal for the “Millennium Tower” was approved by the Millennium Commission in September 1995. Later that year, Portsmouth City Council published a development brief outlining the broad requirements. The concept was to create a public and educational facility to celebrate the new Millennium. Public exhibitions and a special edition of Portsmouth City Council’s magazine, Flagship revealed the three design proposals for the City residents to choose from; the Globe, the Spinnaker and the Triple Tower. 60% of people voted for the Spinnaker Tower hence it became the chosen design, reflecting Portsmouth’s unique maritime heritage. Political, financial, contractual and construction problems delayed the project, and construction of this striking structure actually commenced in November 2001. It wasn’t plain sailing and there were many challenges for the highly dedicated and professional teams of architects, designers, engineers, builders and operators. However, to much acclaim, the Tower finally opened in October 2005. CONSTRUCTION Standing in the 110m high Sky Deck on a windy day, open to the elements you really do get a sense of the remarkable engineering skills that were required to build this unique structure. The Tower’s structural engineering is extremely complex, its complicated shape and design required many mind bending geometric calculations and not least, before the Tower was built, the space it now occupies was sea!
The Tower’s base was constructed first by driving 84 reinforced concrete piles into the sea bed, then building what was described by engineers as a concrete ‘cake tin’ on top. More concrete was pumped into this to form its solid base above the water level. These foundations support the weight of the Tower and provide a buffer against accidental impact from a ship. The Tower’s ‘legs’ were also constructed from concrete but using different process called ‘slip forming’. This involved pouring 11,000 cubic metres into two shafts, one for each leg. Every 12 – 14 hours, as the concrete dried, the shaft was moved upwards. 75 metres were completed in just 4 weeks with the entire height of the legs taking 3 months. Whilst ‘slip forming’ is not a very unusual method, it is believed that the Spinnaker Tower construction was the first time such a method had been used on hexagonal legs not at right angles to the base – the Tower’s legs are constructed at an angle of approximately 2 degrees, eventually merging at View Deck 1 level.
FACT FILE The Tower has been a huge success and has received over 2 million visitors since opening. The high speed internal lift travels at 4 metres per second, taking you to the View Decks in just 30 seconds. The concrete used to build the Tower would fill five-and-a-half Olympic-sized swimming pools. The Tower is founded on 84 piles, the longest of which runs 50m into the ground – the equivalent of Nelson’s Column. The total weight of the Tower exceeds 30,000 tonnes. The 27m spire weighs 14 tonnes and was carefully lifted into place by crane. 1200 tonnes of structural steel used to form the Tower's distinctive bows is the equivalent weight of 12 blue whales. 115 metres up and in high winds, the Tower can flex approximately 150mm. There are 570 steps from the base up to View Deck 3, the Sky Deck.