7. Draw a CE diagram showing different factors that could contribute to delaying the project.

8. describe how risks are reduced over the lifespan of a project such as this one

9. with reference to the concerns expressed upon completion of the construction, discussion

statement. "Risks always relate to the future. There is no such thing as a past risk"

Case - Reference

Newtown, South Africa is a suburb of Johannesburg that boasts a rich cultural heritage. As

part of an attempt to help rejuvenate Newtown, 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 (Figure 10.10) 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 dad 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 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 aggregate and cement in the concrete mixture

segregating in the pylon tubes before the concrete solidified, witch 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.

Figure 10.10

Nelson Mandela Bridge. Johannesburg.

Source: Stock.

CASE 10.3 THE NELSON MANDELA BRIDGE33

PART II PROJECT LIFE CYCLE

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 labor-hours project. The pump never failed and

constriction 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 feit the the cost 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.