The band is starting to play louder at the awe-inspiring Msikaba Bridge project, according to Concor project director Laurence Savage, of this pioneering structure. The Msikaba Bridge forms part of the South African National Roads Agency Limited’s (SANRAL’s) N2 Wild Coast project and is being constructed by the CME joint venture, a partnership between 100% Black-owned Grade 9CE South African construction companies 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,” explains Savage. “We are now entering some exciting but technically challenging phases.”

The first of these is the post-stressing of the anchor blocks, to ensure the transfer of load exerted by the stay cables is well distributed through the blocks. 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.

He highlights that the post-stressing option is a modern and efficient strategy that reduces the need for reinforcement steel – which could have congested the blocks and made it difficult for the concrete to fill all the voids. 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 weeks 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 m mark,” he says. “There are 17 inserts for each pylon; these are steel rings weighing 8 t to 10 t each, which are concreted into place one after the other until the pylon reaches a height of about 122 m.”

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 notes 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 – itself a highly technical task – to start after the first five inserts are installed, which is likely to be in the second half of 2024.

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 m3 of concrete in a single pour, with a very strong 65 MPa mix,” he says. “This will also demand a high density of reinforcement steel, weighing 160 t.”

CAPTIONS

TECH PIC 01 : The flagship Msikaba Bridge near Lusikisiki in the Eastern Cape is now reaching a more technically challenging phase.

TECH PIC 02 : The Msikaba Bridge forms part of SANRAL’s N2 Wild Coast project.

TECH PIC 03 : High above the Msikaba river in South Africa’s Eastern Cape, a new icon on the rural landscape has reached an exciting stage.

TECH PIC 04 : Once completed the two pylon spires for the Msikaba Bridge will create two elegant pinnacles that are bound to inspire admiration from travellers and communities for many miles around.

TECH PIC 05 : The pylon spires of South Africa's Msikaba Bridge mega project are on their way up, soon to tower almost 130 m high at each side of the near 200-m-deep river gorge.

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