IT COULD be the diciest cranage on any Australian CBD construction site, and the most visible. The climbing crane on Brisbane’s Aurora Apartments building protruded from the 69-level residential tower with only a 6m to 7m clearance to the street, being outside current practice exclusion zones.
The prominence of the 1000E Favco climbing crane was also due to the tight building site fronting a busy traffic junction where the city’s northbound traffic along Eagle Street meets the main shopping artery of Queen Street and Wharf Street.
Proximity of the crane to the street presented problematic public protection and safety issues when climbing and taking it down. At a height of 240m above the ground, it would be impossible to gauge how far a dropped bolt, nut or washer could bounce or what it might hit. Short of closing Brisbane down for a day, safety factors had to be designed into the frame of the crane and strict assembly and dismantling procedures observed.
No road closures
The consent authority, Brisbane City Council allowed the contractor, Bovis Lend Lease to close off the street footpath for crane operations and construction activities during the day and tunnel pedestrians beneath the site. The footpath was opened again after hours. But the Council would only allow street closures for three to four hours on a Saturday morning between 6 am and 11 am. This was a totally improbable situation for Bovis Lend Lease (BLL), so a solution to climbing the frame at any time without road closures was devised with crane hire subcontractor Lindores.
The “no falling parts” system involved assessing what movable parts were involved – such as nuts, bolts, washers – then enclosing the sides of the frame with appropriately sized mesh panels and attaching a mesh catch basket beneath the rigger’s platform which had an infix mesh.
Where the crane was tied to the building no bolts were used. Instead pins with chains – specially manufactured fastenings – attached the crane onto the tower above. Anywhere there would normally be a bolt or loose connection it was replaced with a chain or pin, so they could not drop. The crane was jumped about 10 times in the tower construction. Without the failsafe system, this would have meant closing off a CBD street for a day, each time.
For taking the crane down, the mesh frame, catch basket system ensured loose parts were captured. A crane dismantling sequence was drawn up by Bovis Lend Lease with detailed diagrams and script in a nine-step process.
The methodology described unbolting procedures, then chaining the tower section onto the monorail, releasing the chains and lowering to the street. In the same process, releasing the chains to the bolts on the climbing rams and lowering them.
The challenge was to handle the two legs of the crane at the crane tie, the pinned connections from the tie to the yoke, the yoke, chain blocks, and crane shim plates. A group of about 12 riggers using compressed air driven wrenches carried out the work.
Trades behind screens
BLL were able to use only one crane because of an innovative structural construction system. A jump form system built all the vertical and horizontal concrete elements; placed the reo across the whole of the tower floor plate including the lift tower and then lifted it all, in four-day cycles. A series of 22 pairs of hydraulic jacks lifted the whole of the formwork, along with concrete pump, trailing decks for the lift, suspended protective screens and shutters in 23 lifts during the construction period.
With all trades encapsulated behind screens, the finishing trades were in place before the next jump. The intensity of the four-day cycle meant that the crane schedule only had three half-hour spare capacity slots in that time. There was no material storage at ground level; a waiting zone and a loading zone shot all materials straight into the job. Subcontractors did have basement site offices. Two Alimak hoists up to jump form and five rotating loading bays were pivotal to materials handling on the building.
Source: Construction Contractor