Spinnaker Tower

The Spinnaker Tower in Portsmouth opened to the public in October 2005. Rising 170 metres above sea level, the Tower forms the centrepiece of the Portsmouth Harbour Renaissance Project. Scott Wilson was appointed as structural designer and lead consultant as part of a design and build contract let by Portsmouth City Council to Mowlem plc in the latter part of 2002. A significant proportion of the funding for the project came from the Millennium Commission.

The Spinnaker Tower is the tallest publicly accessible structure in the UK outside London. Visitors to the Tower are transported to observation decks up to 110 metres above sea level, allowing spectacular views over the city, the busy naval and commercial harbour, the surrounding countryside and the Isle of Wight.

The steel, concrete and composite structure comprises a reinforced concrete A-frame and two very large curved steel box girders which start at ground level behind the Tower, rise to intersect as they pass between the legs of the A-frame and billow out towards the sea to form the characteristic spinnaker shape that gives the structure its name. A composite spire forms the needle-like top to the concrete A-frame.

The size and location of the site and the very unusual shape of the structure combined to pose some very interesting design challenges. Not surprisingly, the construction condition was critical to the design in a number of respects. In addition, ship impact, wind dynamics, wind-induced fatigue and consideration of human perception to wind-induced movements at observation deck level were addressed in the design.

The Tower expected to attract more than half a million visitors annually within a few years of its opening.