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South Africa: Msikaba Bridge construction moves into highly technical phase

The pylon spires of South Africa's Msikaba Bridge mega project are on their way up, soon to be almost 130 m high at each side of the deep river gorge. (Image source: Concor)

Concor Construction the contractor for the Msikaba Bridge in South Africa, has indicated that progress is continuing to be made on the project and they are now entering a highly technical phase

The erection of the bridge is part of the South African National Roads Agency Limited’s (SANRAL) N2 Wild Coast Project and is being constructed by CME JV, a partnership between Concor and MECSA.

“The last two years have been spent completing the four 21,000 t anchor blocks and progressing the elegant bridge pylons on each side of the gorge,” explained Laurence Savage, project director of the structure. “We are now entering some exciting but technically challenging phases.”

The next steps include the post-stressing of the anchor blocks to ensure the transfer of load exerted by the stay cables is well distributed. Embedded 14 m deep into each block, the post-stressing is profiled as a large ‘U’ shape to mobilise the dead mass of the anchor block being pulled up by the stay cable at the top. The post-stressing option is a modern and efficient strategy that reduces the need for reinforcement steel, according to Savage. The locally procured post tensioning strand cables at each of the 17 anchor points in each block are stressed up to around 500 t by a specialist company. The process is expected to take two to three weeks for each anchor point.

“The next major step will be installing pylon inserts into the pylon’s structure as it rises above the 86 metre mark,” Savage continued. “There are 17 inserts for each pylon; these are steel rings weighing 8 to 10 t each, which are concreted into place one after the other until the pylon reaches a height of about 122 metres.”

The pylon inserts are used as the anchors from which the cables run as back-stays to the anchor blocks, and as fore-stays to the bridge deck. However, Savage noted that not all the inserts have to be in place before the launching of the deck can begin. Careful planning will allow the deck launching to commence after the first five inserts are installed, which is likely to be in the second half of 2024.

Beyond this, another demanding aspect of the bridge’s latest phase will be the construction of the ladder deck. Being the first steel deck segment of the bridge, the ladder deck is to be cast in concrete into the foundation of the pylon and will be the largest continuous pour on site.

“We will cast 700 cu/m of concrete in a single pour, with a very strong 65 MPa mix,” Savage concluded. “This will also demand a high density of reinforcement steel, weighing 160 t.”

Learn more about the impact the Msikaba Bridge project is having in South Africa in the latest issue of African Review.

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