The three slim towers are critical to the unique appearance of Queensferry Crossing. It is no coincidence they mirror and complement both the three massive steel-trussed cantilever support towers of the Forth Bridge and the slender suspension cable towers of the Forth Road Bridge.
In terms of scale, at 210m above Mean High Water level, the three towers are the tallest of any UK bridge. The top of the towers are 147 metres above deck level, 50 metres higher than the main towers on the Forth Road Bridge.
The towers are hollow and are formed from reinforced concrete. The outer dimensions of all three towers are equal, measuring 14m x 16m at their base and tapering gracefully to 4.5m x 7.5m at their pinnacle.
The towers were constructed in stages using an innovative climbing formwork system, founded inside 1,200 tonne steel concrete filled caissons with a diameter of 30m as a base. The base of the North Tower was protected behind a cofferdam. The bases of the flanking towers were fixed on top of concrete plugs inside the caissons fixed onto the bedrock, and the concrete was poured underwater to a height of 26m, with the South Tower setting a record for the world’s largest ever continuous underwater concrete pour. In total 40,000 tonnes of concrete was batched on site and delivered by barge continuously, day and night over a 15 day period. The bridge project used a total of 500,000 tonnes of high-quality concrete.