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The new Queensferry Crossing near Edinburgh, Scotland (the longest three-tower cable-stayed bridge in the world) has modular expansion joints with a movement capacity of 2300 mm – among the largest joints of this type ever manufactured and the first time modular joints of such dimensions have been supplied with noise-reducing surfacing
This extraordinary bridge across Scotland’s Firth of Forth has a total length of 1.7 miles (2.7 km), with two main spans of 710 yards (650 metres) each. It was constructed by an international consortium including American Bridge from USA, Hochtief from Germany, Dragados from Spain and Morrison Construction, originally from Scotland. The final design was undertaken by a joint venture comprising Grontmij, Gifford, Ramboll and Leonhardt Andrä & Partner, based on a specimen design by a Jacobs Arup joint venture.
The bridge’s design necessitated the use of enormous expansion joints to accommodate longitudinal deck movements of 2300 mm at the south abutment and 1700 mm at the north abutment. With its great ability to also facilitate transverse and vertical movements, and rotations about any axis, joints of the modular type were the preferred choice. To address the need to avoid disturbing noise from vehicle wheels as they traverse the joints, it was decided to equip the joints with noise-reducing surface plates (so-called “sinus plates”). The largest of these TENSA®MODULAR expansion joints have 23 movement gaps, each gap allowing 100 mm of movement due to the sinus plates which bridge the individual gaps creating a continuous surface for vehicle tyres. The sinus plates also reduce the noise generated by the over-rolling traffic, by up to 80%, compared to a standard modular joint.
To further limit noise from the expansion joints as traffic passes over them, they were equipped with a second noise-reduction feature, which tackles noise emanating from the underside of the joints. This type of noise transmission can be addressed by enclosing the space beneath an expansion joint (of any type) using flexible, noise-absorbing membranes. The ROBO®MUTE system applied to the underside of the expansion joints was found in testing at the bridge to be very effective in this regard, with peak noise levels reduction by 15 dB(A).
The design of the bridge, with separate continuous superstructures for northbound and southbound traffic, called for two expansion joints at each abutment, each with a length of over 17 m. To avoid the need to weld joint sections together on site, the expansion joints were delivered from the mageba factory in Shanghai to the site in Scotland with their total length of over 17 m, a width of over 5 m and a weight of 55,000 kg – a challenge in its own right.
With record-breaking expansion joints in this record-breaking bridge, this project is justifiably a source of pride for Scotland and for all those involved in its construction – including mageba.