Msikaba Bridge, South Africa
The Msikaba bridge is a cable-stayed bridge, currently under construction, spanning the Msikaba River, near Lusikisiki in the Eastern Cape Province of South Africa. The bridge forms part of the N2 Wild Coast Road (N2WC) project, which aims to improve the travel time between Durban and East London for light and heavy freight vehicles.

Earmarked as one of the government’s strategic infrastructure projects, construction is already proving its worth through the promotion of economic activity, community development, service delivery and job creation at both a regional and provincial level.

580
m
deck span
192
m
high
787000
m2
of earthworks cut

Solution

One of the key aspects of the bridge is its two identical, inverted Y-shaped, reinforced concrete pylons. Each of the 127 m tall pylons comprises two inclined legs, straddling the roadway below, and a tall cylindrical spire. The spires have a diameter of 6 m at the bifurcation, where the two legs meet, tapering to 4.5 m at the top. Anchored into each pylon are 17 pairs of main stay cables (connected to the deck) and 17 pairs of back stay cables (anchored 130 m behind the structure). The cables are anchored by means of 17 internal structural steel anchorage liners starting at a height of 88 m.

Steel anchorage liners form a critical part of the structural system as they transfer the loads, generated by the superstructure, through the stay cables and down into the pylon shafts. The mechanism of load transfer between the steel anchorage liners and the concrete pylon is through shear stud connectors.  Each 2 m tall liner has approximately 400 shear studs and weighs approximately 10 tons. The largest liner at the top of the pylon transfers a total of 1400 tons from the pair of main span and back span cables to the pylon. The combined load from all of the liners results in a load on the pylon of more than 20 000 tons at the top of the pylon inclined legs. The liners have been manufactured locally, off-site at a facility in Witbank.

Temporary works

The remoteness of the project as well as the logistics of travelling from the northern side to the southern side – a three-hour drive – means that a cable way has been installed as part of the temporary works. A mono-rope cable system, equipped with a six person cabin is being used to transport people and small amounts of material from one side to the other. The cable car takes only eight minutes to traverse the gorge resulting in a significant time saving for all crew on site.

The project has also been aided by an agreement between the South African National Roads Agency (SANRAL) and the Magwa Tea Estate, the biggest tea estate in the Southern Hemisphere. Magwa has provided 8ha of land for the Engineering teams accommodation camp which houses the majority of SMEC’s site staff. This forms part of a legacy project, whereby SANRAL agreed to refurbish existing houses on the estate and provide additional prefabricated houses as part of Magwa’s future eco-tourism plans.

SMEC is providing construction monitoring and technical support services for the project which includes short sections of approach roadworks on either side of the bridge, as well as five tributary structures. The composite steel and concrete deck of the main bridge is 22.8m wide and includes foot walks to the outer edges of the deck.

Impact

President Ramaphosa visited the site in September 2021, stating that the project would generate between 21,000 and 28,000 indirect jobs during construction and 8,000 direct full-time jobs once completed. Once complete, the route will be 69km and 85km shorter than the current N2 and R61 routes, respectively, and, owing to its shorter and flatter alignment, between 1.5 to three hours faster for light and heavy freight vehicles.

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