Towering performance

The Melbourne Cricket Ground in Victoria, Australia is being redeveloped for the 2006 Commonwealth Games. But because it is a major venue for cricket and Australian football in the province, it has needed to keep at least 80% of seats open for matches during construction.

This meant that all construction had to take place from the rear of the building, with no incursion onto the arena. Grocon, the principal contractors for the project, initially planned to undertake the job as a staged project, with each of the five stages requiring two tower cranes and a large mobile crane.

However Grocon plant manager Bruno Morosinotto believed that there was a better solution. He investigated the Favco M1280D, a 100t capacity crane that had worked on an upgrade of the Burrinjuck Dam in New South Wales. In the end, the crane’s owner, Gordon Marr, of Marr Contracting, offered it and a 200t capacity M1680D.

Grocon also hired two 150tm-class M440D tower cranes from Favco, and planned so that all cranes could do the traditional tower crane work, and the larger two cranes could also handle the heavy lifting normally done by crawler or mobile cranes. A 250t crawler crane is being used to erect and dismantle the tower cranes, and 200t mobile crane has been used while a tower crane is being relocated, but otherwise the tower cranes have handled the heavy lifting. Each tower crane will have to be relocated once during the project. Towards the end of the project, a Favco 1500 will also be erected.

Using tower cranes offers the contractors several advantages over crawler cranes. The tower cranes stand outside the footprint of the grandstand, leaving the stadium open for use and, unlike mobile cranes, can reach almost all of the site. They need little of the ground preparation required by mobile or crawler cranes, estimated to cost up to $A 10m ($tk). They have small footprints that allow more area for storage and movement of materials and equipment. With 50t winches, the tower cranes have single-fall reeving and so a fast hook speed. The lift chart is good for 360°. The tower cranes reduce congestion on site and offer a better vantage point for crane operators, which improves safety.

The foundations for the tower cranes are deserving of special mention. They were designed by Damian Hibbert of DJ Hibbert Construction Engineers (DJH). The 6.5-metre square, 2.6-metre thick pile caps are founded on four bored piles each 1200mm in diameter, and up to 18 metres deep. As the ground would not support the weight of a bottom tower and anchorage feet, DJH devised a lightweight starter frame with reusable rock bolt anchors instead of a cast-in starter leg system costing around $25,000.

The starter frame keeps the hold-down bolts straight during the pour. The foundation load is around 10 times the load of a standard tower crane, and there can be 1100mm of secondary movement in the tower, under full load. For the M1280D the bolts are tensioned to 90t, while for the M1680D the bolts are tensioned to 110t.

Marr says that he believes that large tower cranes should be viewed not only as the crane to use for a long-term project, but also as an alternative for heavy lifts on sites where access is restricted. On a short boom the M1280D will lift 100t at a 25m radius, and the M1680D will lift 200t at a 15m radius. These cranes are comparable to 400t-class crawlers such as Liebherr’s 400t capacity LR 1750 (130t at 26m radius with 28m boom) or Manitowoc’s 450t capacity 18000 (146t at 26m radius with 37m boom).