The Queensferry Crossing Bridge: Strand Post-Tensioning Systems ensure Long-Term Connection

The existing Forth Road Bridge built in 1964 near Edinburgh in Scotland is an important road connection across the Firth of Forth – the Forth River Estuary into the North Sea. The 2.5km long suspension bridge was originally planned for 11 Million vehicles per year; however, it is now being used by approximately 24 Million vehicles per year.

That is why the new Queensferry Crossing Bridge is being built parallel to the Forth Road Bridge and to the railway bridge that was opened in 1890. Once completed, the 2.7km long bridge will accommodate the M 90 Motorway on 4 lanes and will be the world’s longest stay cable bridge with 3 pylons. Each of the 3 pylons is 207m high.

The individual spans of the 2,055.50m long stay cable bridge measure 104m, 223m, 650m, 650m, 223m, 104m and 101.5m. The 180,000t composite bridge deck is made up of 110 single box precast segments, each 16.2m long. The cast in-situ North Approach Viaduct consists of 12 single box segments with a total length of 145.80m and approx. 60m long pier tables on each of the pylons. In total, 150,000t of concrete and 30,000t of steel are used for the bridge.

To prestress the bridge deck and the central tower, DSI supplied internal Type SUSPA Systems bonded Post-Tensioning Systems. The main part of the work was carried out in prefabrication sheds on site, where the prefabricated tendons were installed as transverse prestressing into the precast concrete segments. The prestressed segments were then lifted using a cable system.

The designer also used the DSI Post-Tensioning System to provide the proper connection between the individual segments of the central pylon. This was achieved by inserting transverse and longitudinal tendons through the pylon and anchoring them inside the box girder.

An important feature of the system is its air-tightness which was implemented according to National Scottish specifications. In total, 3,000 Type 6-5 SUSPA Systems strand tendons with flat plastic ducts, 20 Type 6-9 strand tendons, 60 Type 6-12 tendons and 58 Type 6-19 strand tendons were used.

Together with the main contractor, DSI supplied a system the high performance of which was confirmed by numerous tests during construction work.

DSI also supported the contractor with engineering services as well as a full installation package including tensioning and grouting.

The experienced DSI employees successfully complied with the tight execution schedule.

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Transport Scotland, Great Britain