Coffs City Cranes (CCC) was engaged by builder R&D Spagnolo to erect 34 tilt-up panels at the Wet Seal Development in Forge Drive, Coffs Harbour (NSW). Greg Keane reports.
The panels ranged from 3t to 22.68t in weight, 830mm to 7500mm in width and 8230mm to 8580mm in height. The size of the largest panels ruled out precast as an option.
CCC supervisor Sam Smith undertook extensive on-site liaison with the builder and Fine Form Precast (which was engaged by the builder to form the panels), and he regards the planning as the most difficult but critical aspect of the job.
The back wall of an existing shed was within 300mm of the new shed panels, so tilting panels into position was not an option. If tilting was reversed to stand panels in the opposite direction, this would have made it impossible to de-rig the lifting gear from the panels once they were positioned, and would have meant that the crews had to brace panels on the dead man side.
The only option remaining was to do a crane transfer, with one crane standing the panels and another crane lifting them into position.
A further reason for this option was that, with the size and weight of the panels, there was a likelihood that picking up the panels with top lifters would damage, crack or even snap the panels when they were released from the slab.
As engineers would not allow cranes to set up on the slab, this meant that a 220t crane was required to provide sufficient capacity at the required reach to place the panels for the back wall, which were the heaviest. CCC did not have a crane of this size, but has a working arrangement with Mid Coast Cranes to access its 220t crane when it requires this size of crane.
Planning the locations for panels to be poured to firstly allow the CCC’s 110t crane to stand the rear wall panels and then ensure that the 220t crane was within radius to place them required considerable thought.
With large voids for windows and doors in many of the panels, considerable engineering was required to position additional reinforcing bars in critical areas, and to optimise the location of the lifters to minimise the risk of damage to the panels.
While a painted finish was to be applied to the panels after erection, care was taken during erection to ensure there were no gouges, scratches or chips on the panels.
Lifting of all panels was undertaken over two days. With the large sail area of many of the panels, the weather forecast was taken into account in planning the lift dates, and wind conditions were constantly monitored throughout the lifting program.
The 110t crane was configured with 30.9m of main boom and 35t of counterweight, while the 220t crane had 34m of main boom and 71t of counterweight. For the transfer lifts, the 110t crane was rigged with a 35t centre lift spreader bar; with six equalising sheaves and ropes and eight 5t swiftlifts. The 220t crane was rigged with two 15t equalising sheaves and ropes; along with four 10t edge lifters.