e-mosty September 2017: Mersey Gateway Bridge. Arenales Bridge. Mersey Gateway Bridge. Arenales Bridge. BLWT. - Page 12

3.3.4 Cables The bridge deck, with a combined load-bearing weight of more than 53,000 tonnes, is supported by 146 stay cables. There are 62 stay cables attached to the South pylon (31 on each side), 54 attached to the North pylon (27 on each side) and 30 attached to the Central pylon (15 on each side). The cable sheaths are helix-shaped to prevent vibrations from wind and rain and were tested in wind tunnels. They vary in length; with the shortest measuring approximately 41m and the longest measuring 226m. Once the deck concrete reached the required strength, the stay cables were installed. The first two strands were threaded through the stay pipe, the pylon crane lifted the pipe up to the anchor point in the upper pylon where the top ends of the strands were fixed into place. Then a winch system within the stay pipe was used to winch the remaining strands up one by one. Once all of the strands were installed they sit in parallel inside the stay pipe to form the stay cable. The bottom ends of the strands were then attached to the anchor point in the bridge deck and stressed using a hydraulic system. This enabled to get the correct level of tension needed to support that segment of bridge deck. More than 1300 km (810 miles) of the strands were used for the project. The strands were delivered to site in compact coils. Every single strand was installed individually, combined to achieve a rate of 6 stays per week. Each stay cable consists of between 41 and 91 individual steel strands that sit inside a stay pipe – the outer casing that provides protection from weather- related corrosion. Each strand contains seven wires, which are galvanised, waxed and coated. Figure 12: The first stay cable being lifted into position by a pylon crane at the South pylon Figure 13: Steel strands can be seen inside the light green stay pipe, which form the stay cable 3/2017 Figure 14: First stay