Award-winning crane project … from the past

Back in 1998 we ran an article about an award-winning, unusual crane project in Auckland that was so unique it featured at length in an international crane magazine.

FLETCHER CONSTRUCTION HAD a challenge – removing a tower crane some 330 metres up on top of the Sky Tower in Auckland.

They called the project ‘Down to Earth’ and it was judged the 1998 Power Crane Association UDC ‘crane project of the year’.

The Liebherr 185HC/256 had been installed atop the tower in mid 1995 and the removal method initially favoured was to use a derrick in the form of a Chicago Boom attached to the tower mast. Other proposals included employing a large helicopter used for logging in the South Island, or a flying-fox system from up on the mast to a suitable anchorage on the ground.

When the crane was being prepared for the project, additional brackets and links were added to enable the jib and counter jib to be removed section by section if required. This, however, was not to be the case.

A 1:20 scale model of the tower crane, the Chicago Boom, the upper part of the tower (the pedestal) and the first four sections of the mast was built and used to evaluate and demonstrate the methods for the tower crane removal, and for the removal of the removal crane.

Early on it became obvious that the combined winch and electro-hydraulic power pack unit used on the Chicago Boom on the 30-floor ASB building was just too big and heavy to take up, as it weighed more than 8000 kilograms and stood more than three metres high.

Clearly, what was required were individual electro-hydraulic power packs for each of the two winches, with the power packs built in a modular form for ease of removal at the completion of the crane removal.

All the removal gear also needed to be able to fit into the Sky Tower’s goods and services lift. Before the boom went to the site, additional lifting lugs were fitted for ease of erection and removal of the boom. As it was impractical to fit back-stops, a piece of 20mm ply was fixed to the rear of the boom to prevent damage to the lacings in the event of the boom being blown back when operating at a minimum radius and hitting the upper sheave block attached to the mast structure. This protective feature was never put to the test; the only purpose it served was to make it awkward for the riggers climbing up the boom.

This is how the timetable of the tower- crane removal programme unfolded through the first months of 1998.

March 10: The boom, winches, power packs, control and electrical cabinet were delivered to the site and a start made on setting them up in their allocated positions.

March 27: The boom was assembled at road level to its full length of 22.35 metres. The boom was lifted into position on the previously attached swing unit and the boom foot pins fitted. Before fitting the climbing frame for the final climb, the cat-walks on the side closest to the tower were replaced by purpose-built ones to enable them to clear the mast when climbing the crane down.

March 29 & 30: The Liebherr was top climbed five sections and the load tested with an M&I engineer surveyor present.

March 31: Further test running of the boom and winches was conducted with loads being run up and down over the full height, about 220 metres. After the hoist rope had settled in, a full speed run was made with 2000 kilograms on the hook.

April 1: The boom was load tested to the satisfaction of an M&I engineer surveyor.

April 2: The Liebherr was occupied all day with a myriad of last-moment lifts for various subcontractors.

April 3: Top-climbing down began with six tower sections being removed and lowered to the ground. Though the crane was no longer free to slew 360° because of the mast, it was stowed with the slew brakes clamped on by means of G clamps. In addition, the crane was mounted on 256 HC tower sections and carried only a relatively short jib of 30 metres. Further, it was close to a building tie.

April 4: The crane was climbed down a further seven sections and two building ties and collars removed. The modified access platforms on the climbing frame cleared the various ducts and brackets on the tower by about 50mm.

April 5: Climb down and removal of a further five tower sections was achieved. Now the crane was climbed down as far as it could go and within reach of the Chicago Boom. The weather forecast for the following day was not good so storm guys were fitted from the crane’s jib down to the roof of the upper observation deck in addition to having the slew brakes locked overnight.

April 6: The rope reel and winder for the hoist rope was set up on the upper viewing platform. The counterweight removal ropes were taken up to the counter-jib. The wind was gusting up to 48 kilometres per hour.

April 7 & 8: Wet and windy.

April 9: All 745 metres of the hoist rope was reeled up. The counterweight removal frame and ropes were fitted and everything was prepared for removal.

April 10: Removal of the Liebherr’s counterweight began. As the Chicago Boom could not reach the weights and because they were way outside the upper viewing platform roof, it was decided that the weights would have to be fleeted in.

April 11: The Liebherr’s 6100 kilogram, 30-metre jib was lowered until it could be landed on two temporary shoreload towers seated on the outdoor observation deck. The jib was ‘broken’ into its component parts then lowered one at a time past the pergola around the observation deck and down to the ground. The hoist winch drum was removed and lowered, as were the hoist winch frame with motor, gearbox and control cabinet. Next came the tower head and counter jib.

April 12: The outer section of the counter jib was lowered to the ground, followed by the three counterweights after the Chicago Boom was slewed to the right. The cab section of the Liebherr was then removed and lowered to rest on two UBs on the roof of the upper viewing platform. Because the 5090 kilogram weight was too heavy for the radius required to clear the pergola, the two slew motors and gearbox assemblies (960 kilograms) were removed and the cab section was sent on its way. The two motor and gearbox assemblies, slew mount and slew bearing, and a tower section all followed.

April 13: The front gate and platforms of the climbing frame were removed and lowered to the ground, then the climbing frame itself, four tower sections and a tie collar complete with struts. The crane had now been cleared down to the top of the concrete plug. This plug consisted of a 1600mm-thick concrete pad between the top of the pedestal and the base of the steel mast. Two passed through the outer deck attached to the plug, requiring this section of tower to be cut off and scrapped.

April 14: The crane tower was cleared ready for removal below the plug, and tower bolts slackened. The tower was then raised 20mm on its own internal climbing gear. Cleats were welded on to the chords above the plug so that when the mast was lowered there was a gap of 20mm between the bottom of the captive tower section and the top of the one below it. This was the working clearance to allow the tower section immediately below the plug to be removed. Temporary steel structural members, passed through the tower during construction of the pedestal, were removed by steel erectors using chain blocks and the Chicago Boom.

This article first appeared in Contractor’s February issue.

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