Y-shaped pylons one of Msikaba’s distinctive features

The Msikaba Bridge forms part of Sanral’s N2 Wild Coast project and is being constructed by the CME JV – a partnership between Concor and MECSA, both 100% black-owned Grade 9CE South African construction companies.

This is the largest cable-stayed bridge to be built in South Africa, and probably one of the most complex engineering bridge projects yet executed in Africa,” explains Laurence Savage, Concor’s project director on this contract. Spanning the Msikaba River, the deck will measure some 580 m in length, bridging the close to 200 m deep gorge below. Each of Msikaba’s two pylon spires rests on inclined legs that meet 21 m from the start of the bifurcation, which extends a full 11 m. At 32 m, the first section of the spire – starting with a diameter of 6 m – is uninterrupted for 55.7 m and comprises 14 slipform lifts. Then begins the inclusion of 17 anchor inserts over the next 35 m of the spire, which reaches a height of 124 m, converging to 4 m in diameter. These anchor inserts accommodate the 17 cables that run from the anchor blocks, located behind each pylon to the spire, and then down to the 580 m long bridge deck.

“To accomplish the lifts, we are using a jacking system for the formwork shutters, with eight jacks around the circumference of the spire,” Savage explains. “Each lift is 3.6 m conducted at intervals of about two weeks per lift and we are making steady progress, with quality and safety being paramount.”

Like the legs of the bridge pylon, the reinforced concrete spire – with 1 m thick walls – is hollow to reduce weight and is formed in a tubular design that significantly improves its strength-to-weight ratio.

Intensive programmes

“Indicative of the precision engineering being employed on this project is the number of activities that must take place at the same time – in a confined area,” Savage explains.

“By the time we have completed the fifth anchor insert, for instance, we will have begun the launching of the first deck segment – followed shortly by the second and third segments. While these activities are taking place, the spire and inserts will continue to be erected and cast,” Savage concludes.