Winds hamper 50 m lift; forced to go 16 days

A daunting 50 m lift of the control tower at South Africa’s new King Shaka International Airport held fast as winds threatened the entire operation in November. So hampered was the operation by KwaZulu-Natal’s adverse weather that month that the scheduled eight-day operation dragged into 16 days.

Keeping the lift steady was PC strand out of Scaw’s Wire and Strand (W&S) division, as well as a host of other stabilising and safety measures. The tower weighs 300 t and has a 20 m diameter. Says Ahmed Patel, W&S’s national sales manager, “The strand was supplied in 1,2 t with a right-hand lay configuration and another 1,2 t with a left-hand lay. The combination of the two configurations prevents twisting of the strands during a lifting operation.”

W&S had supplied 12.90 mm, Grade 1860 MPa PC strand to Tsala-RMS Construction Solutions to conduct the lift, after VSL had cut it into 60 m lengths.

Four sets of wheels and wedges were located between the cabin and concrete tower by Tsala-RMS to restrict lateral movement caused by the wind. Sophisticated equipment.

Four lifting points were mounted equi-axed at the top of the column. At each lifting point 12 strands were employed and secured with 175 t jacks. The pressure applied at each of the four jacks was equalised using a single 4-outlet pump.

Charlie George of Tsala-RMS states: “Due to the cabin having been glazed at ground level, it was necessary to maintain a stringent maximum vertical tolerance of 20 mm. This was monitored by the use of a sophisticated electronic device which recorded the variance in level at four points on the perimeter of the structure. The data was relayed to a display monitor located at the central pump by means of a radio transmitter. The vertical position of the cabin was monitored by means of a laser instrument and both the vertical differentials as well as cabin height were recorded at every 100 mm lifted.”

A close up of the anti-twist lay configuration of the PC strand.

Image of the tower illustrating the lift from ground level to the top using 12.90 mm Scaw strand.