Designed by Meisho (Japan), the wheel is being erected by Alfasi Steel Construction using a new 600t Terex-Demag CC2800-1 crawler crane supplied by Tutt Bryant Crane Hire as the major lift crane and its own 150t Sumitomo SCX 1500-2 crawler crane for general lifting and tailing as required. A variety of other cranes from its own fleet or local crane hirers were used as required.

The CC2800-1 was initially rigged with 96m of main boom and 300t of Superlift counterweight, and undertook all lifts from a single lift pad.

Tutt Bryant Crane Hire and Alfasi Steel Constructions spent several weeks in detailed planning for the project, using Autocad for detailed 3D lift studies. The suggested method from the designers involved use of 600t, 400t and 300t pin jib crawler cranes, and this would have been prohibitively expensive, even if all the cranes had been available at the one time: almost an impossibility in the current buoyant Australian market.

An objective of the lift studies was to develop methods that allowed connections to the inner hub and spokes to be made from the side, rather than at the top of the hub, to reduce the lift height and allow smaller cranes to be used to assist the 600t crawler crane, which was required for the heaviest lifts. The methods developed are not believed to have been used elsewhere in the world for similar structures.

The attention to detail and quality control in the planning and construction phases have allowed the erection to proceed smoothly, despite this being the first big wheel built by Alfasi, and the largest designed by Meishi. Understanding the behaviour of the structure at different stages of construction was a continual learning curve.

Because of the poor ground conditions (Coode Island silt, with the water table only 2.5m below ground level), the concrete lift pad was 12m x 11m x 2.5m deep, and founded on 24 piles. The ground over which the Sumitomo travelled was covered with geofabric overlaid with crushed rock.

The observation wheel comprises an inner and outer hub joined by seven spokes, with the axis supported on each side by tripod stands. The tripod legs comprise a 56.2m long, 59.8t vertical column and two bracing columns; one being 58.9m long and weighing 76t, and the other being 72m long and weighing 76t. The legs were fabricated off site and delivered in two halves, with final assembly and painting taking place on site. A capital joined the legs at the apex.

The first tripod erected was furthest from the fixed lifting position, and its vertical leg was erected first. Both cranes lifted the leg from the ground, with the Terex-Demag raising the upper end and the Sumitomo walking the base into position, where it was connected to the foundations. The leg was then held in place using temporary supports.

The last legs

The remaining two legs were erected in a similar manner, although this was complicated by a drain running through the work area. The Sumitomo walked the base of each leg to the edge of the drain, where it was unhitched from the load and walked around the drain. It then picked up the leg again, and walked it to the foundations. These legs were also secured in place by temporary props until the capital was placed.

The second tripod was erected in a similar manner, but because the radius was reduced 32.5m, the Superlift counterweight of the Terex-Demag was reduced to 100t.

The next stage was to pre-assemble the 25m diameter, 8m deep inner hub that weighing 152t. It was built on a temporary assembly stand 14m above the ground, and lifted from there to a height of 67m, where it was mounted in bearings on the capitals. This took 5 hours, and the Terex-Demag crane was at 99% capacity for the lift. The biggest concern was the wind (gusts of 140 km/h had been recorded at a similar time during the previous year), and with the 490m2 surface area of the hub, the safe wind speed for the lift was calculated at 19 km/h.

The final lifts on this project for the CC2800-1 were the seven triangular lattice construction spokes, each 33m long, 10.2m wide at the base, 8m deep and weighing 24.5t.

The first four spokes were installed at the three o’clock position, and the boom was then reconfigured from 96m to 114m length for the final three spokes, which were installed at the one o’clock position. The wheel was rotated between lifts, so that the lifts were undertaken at the same orientation.

The first two spokes were installed as dual lifts using the Terex-Demag and Sumitomo crawler cranes, and all other lifts were undertaken with the Terex-Demag alone, with the Sumitomo supporting a man basket for the riggers connecting the spokes to the hub.

Soft slings were attached to the main chords at the top of each spoke at 4 points, and chain blocks were connected in two locations at one end, allowing fine adjustment of the angle of the spokes to assist with the connection. Each spoke took six hours to install.

Once all seven spokes were installed, small sections of the outer rim were installed to each of the spokes. These rim sections were 12m long and weighed 12t, and were installed using Alfasi’s 150t Sumitomo SCX 1500-2 crawler crane, with its 70t Tadano GR-700EX used for man box access. These sections were installed at the four o’clock or eight o’clock position, with the wheel rotated between lifts using hydraulic winches.

The outer rim was built in sections on the ground, with each section joining a pair of spokes. The sections were approximately 30m long and 6.5m wide, and weighed 32t. When each section was constructed it was walked into position for the lift, using the Tadano GR-700EX and two 20t Franna articulated pick-and-carry cranes.

A 200t all terrain crane was hired in as the main crane for these lifts, with the GR-700EX acting as a tailing crane and Alfasi’s 55t Tadano GT-550EX truck crane supporting a man box for the riggers to connect the rim section. Each section was installed in the seven o’clock-eight o’clock position. The SCX1500-2 was used to tension the top spoke, which sagged when not connected to the outer rim, and 17t of force was required to correct the sag.

The boom of the 200t crane was positioned under the spoke above for the rim section lifts, with only 0.5m clearance between the boom head and the spoke steelwork.

The wheel was rotated between lifts with the hydraulic winches so that all outer rim segments were erected in the same position. Each lift took 5-6 hours.

The main work remaining is to attach hangers to the outer rim to support the 21 observation cabins, and to attach the cabins (each weighing 14t). The cabins will be lifted onto a raised slab that forms part of the permanent works, skated into position and jacked up for attachment to the hangers.