Construction World November 2016

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This reduction allows for the construction of a slanting front face which creates both functional strength for the pylon as well as being aesthet- ically pleasing. Additionally, for the stability of the structure, the pylon base required 20 x 1,2 m piles to be cast each more than 20 m deep to make contact with bedrock below. The pylon also requires five cross beams to assist in torsion control to brace the two legs. These are spaced about 4 m apart and begin at 35 m from the base of the pylon. Once completed the pylon legs will support the heavyweight 27-strand cables measuring up to 88 m long, as well as the weight of the structure, traffic and other calculated exterior forces. Following the final tensioning and completion of the concrete work, the final step in the construction of the bridge will be the addition of a bitumen running course to provide a smooth surface for the Rea Vaya buses, as well as a ‘bolt-on’ structural steel pedestrian walkway. Dependable partnership Van Rensburg’s summation is, “For a job of this size and complexity we prefer to deal with a professional and dependable partner. Form- Scaff helped us overcome some of the challenges associated with working on a project which requires dynamic design solutions in very limited time spans. “A good example is the cable formwork tubes that are cast into the pylon which needed to be lined-up perfectly with the ties at the bottom. This is not an easy task considering the tubes have to be held in place for multiple lifts as the concrete pouring progresses. In the end however we worked on solutions and in collaboration with Form-Scaff were able to overcome these potential pitfalls,” says Van Rensburg. “Another challenge was the balancing and anchoring of the bridge

considering it has an 88 m reach on the Sandton side – and just a 33 m reach on the other. To overcome this, Hatch, the design engineers, called for the construction of a much thicker, solid deck on the short side of the bridge to help counterbalance the weight deficit. The piers also needed to be anchored from the deck level into bedrock on the short side to provide additional stability. Overcoming challenges “Likewise, the solution for the cable formwork tube alignment issue has also been solved and involves slotting the formwork to allow them to be lifted after each pour without interfering with the cable tubes. “Although these were technically challenging, they are just some of the many complex issues that you get on a live site. In my experience the kind of technical support you surround yourself with ultimately determines the manner and success of the solutions created to address them. “Having worked with Form-Scaff on a number of similarly complex projects in the past we are 100% confident in their overall ability to deliver according to the specifications of the project. On this particular site the expertise and technical support provided by them has been pivotal to the success of the project overall,” concludes Van Rensburg.

CONSTRUCTION WORLD NOVEMBER 2016