Newtown, South Africa, is a suburb of Johannesburg that boasts a rich cultural heritage. As part of an attempt to help rejuvenate Newton, the Nelson Mandela Bridge was constructed to link it to important roads and centers of commerce in Johannesburg. Spanning 42 electrified railway lines, the bridge has been acclaimed for its functionality and beauty.
Lack of space for the support pylons (towers) between the railway lines dictated that the bridge design would have a long span. This resulted in a structure with the bridge deck supported by stay cables from pylons of unequal height. The pylons on the northern side are 48 meters high, and those in the southern side are 35 meters high.
The pylons are composite columns consisting of steel tubes that had to be filled with concrete after being hoisted into the vertical position. The decision was made to pump the concrete into the tubes through a port at the bottom of each tube. This had to be done in a single operation. Although the technology for casting concrete this way was not new, the columns were the highest in South Africa, and filling them would set a world record for bottom-up pumping of self-curing concrete.
The pump for the concrete was placed at ground level between the electrified railway lines, which exposed workers to the risks of being near continuous rail operations. The pumping method posed the risk of the stone and cement in the concrete mixture segregating in the pylon tubes before the concrete solidified, which would compromise the strength of the concrete. Another risk was that the pump might fail and result in the concrete solidifying in an uncompleted pylon, rendering further pumping of concrete from the bottom impossible. Two contingencies were considered: an additional pump on standby, and completing the process by pouring concrete from the top of the pylon.
The concrete had to be transported by trucks to the site, which risked interrupting the concrete supply owing to traffic congestion in the city.
Despite working over a busy yard with trains running back and forth, no serious accident occurred at any time in the 420,000 man-hours project. The pump never failed, and construction finished on time. The stay cables—totaling 81,000 meters in length—were installed and the bridge deck lifted off temporary supports, all while the electrified railway lines beneath remained alive. Upon completion of the bridge, some felt that the costs incurred to reduce the risks had been excessive; others held that the risks were too high and not enough had been done to reduce them.
QUESTIONS
1. With reference to the concerns expressed upon completion of the construction, discuss the statement: “Risks always relate to the future. There is no such thing as a past risk.”
2. Discuss the difference between good decisions and good luck.
3. How could a manager protect himself against the risk of making a decision that might later have negative implications?