According to Concor Construction, the contractor that has been tasked with the construction of Msikaba Bridge in South Africa, has recently indicated that the construction progress on the Africa’s Longest Cable-stayed Bridge project is now headed for a very technical phase.
The establishment of the bridge is part of the South African National Roads Agency Limited’s (SANRAL) N2 Wild Coast Project and is being built by CME JV, which is a partnership that was formed between the two firms, i.e. Concor and MECSA.
“The previous couple of years were spent on completion of the four 21,000 anchor blocks and progressing the pylons of the elegant bridge on both sides of the gorge,” elaborated Laurence Savage who is the project director of the bridge structure. “We are currently, diving into some thrilling but technically challenging phases on the bridge project.” He added.
The next phases will entail the post-stressing of anchor blocks in order to ensure that the transfer of the load that is exerted by the stay cables of the bridge is distributed well and evenly. Embedded at a depth of 14 meters into each block, the post-stressing is profiled as one large “U” shape to mobilize the dead mass of the installed anchor block being pulled up by the stay cable at the top.
Post-stressing
As Savage revealed, post-stressing is a modern and very efficient technique that usually cuts the need for reinforcement steel. The post tensioning and strand cables that have been procured from the local market at each of the total 17 anchor points in every block are stressed up to around 500t by a company that has specialized in such works. This process is foreseen to take approximately 2-3 weeks for every anchor point on the bridge project.
Additionally, the next major step will involve the installation of the pylon inserts into the pylon’s structure as it rises more than 86 meters. “There are a total of 17 inserts for each of the pylons; these entail steel rings that weigh 8-10 tonnes each, which are concreted into place one after another until the pylon structure attains a height of approximately 122 meters.
Pylon inserts are usually used as the anchors from which the installed cables run as back-stays to the anchor blocks on the bridge, and as fore-stays to the deck of the bridge. However, Savage pointed out that not all the inserts need to be in place before the launching of the deck can start.
Commencement Date of Launching of the Deck on Africa’s Longest Cable-stayed Bridge
Careful planning is set to pave way the launching of the deck to commence after the first 5 inserts are fully installed. This is likely to be conducted in the second half of the year 2024.
Other than this, another demanding aspect of the latest phase of the bridge will be constructing the ladder deck. Coming as the first steel deck section of the bridge, the ladder deck is to be cast in concrete into the foundation of the pylon and will stand out as the largest continuous pour on the bridge site.
There will be casting of 700 cu/m of concrete in one pour, with an extremely strong 65 MPa mix. This will call for the need of high density reinforcement steel, weighing 160 tonnes.
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