THE tower crane industry in Australia was ‘in turmoil’ last month after a 5 August accident in Melbourne which killed a construction worker. The accident happened on a site run by contractor Baulderstone Hornibrook on Melbourne’s Southbank.
A Favelle Favco M310D luffing boom tower crane was being climbed on a windy day when 20t of moveable counterweight came off and crushed a worker in a nearby Alimak hoist. It is the first known accident of its kind, according to engineers who know this crane well. The cause is still being investigated.
The government occupational health and safety organisation WorkCover immediately ordered an inspection blitz on all tower cranes, a process expected to take weeks and cost millions of dollars in downtime and construction delays.
‘The tower crane industry, especially in Victoria [the state in which Melbourne is], is in a state of turmoil and even more stringent inspections can be expected in the future,’ a leading figure in the Australian tower crane scene told Cranes Today.
An engineer close to the investigation suggested that as the crane type was ‘a common sight throughout Australia’ the accident was unlikely to be attributable to a design fault. ‘To the best of my knowledge there have been no other occasions in 40 years of these cranes in which these cranes have lost a counterweight,’ he said, before adding: ‘The cause is for the coroner to determine.’ The crane involved in the accident was manufactured in 1990, five years before Muhibbah Engineering of Malaysia acquired the name, assets and intellectual property of Favelle Favco. The design of the M310D was not continued under Muhibbah’s ownership.
The M310D is fitted with a fixed counterweight stack at the rear. Under the machine deck there is additional counterweight of 20t which travels on wheeled trolleys along the length of the machine deck. The travel is actuated by wire ropes around sheaves which have one end attached to the trolley and the other to the boom butt. As the boom luffs up the weight moves in and as it luffs down it moves out. The assistance to limiting the over turning moment is described by one engineer as ‘useful but not great’.
These cranes are fitted with climbing frames and jacking mechanisms. When a crane is to be climbed, the next tower section is lifted by the crane and attached to a cantilevered beam with a running hand trolley. The moving counterweight is brought up to the crane tower and latched. The trolley ropes may be removed so that the crane can boom down to balance the structure.
It has been known to happen that at a point at which work must continue to a close-off position, a strong wind blowing onto the face of the boom can hold the boom at a high angle until the wind abates. When the wind eases off the boom can freefall to the extent that luffing rope has been wound off the drum. Such an action will cause strong and sudden movement of the tower structure. The return of the tower to its original seating must be felt by the counterweight trolley. If the locking mechanism failed and there was no other restraint, then the trolley would run off the rear of the machine deck into free fall. If the trolley was fitted with a brake it may restrain the load if the load is within the design parameters of the brake. Further bolted-on backstops would prevent the counterweight and trolleys from falling if the bolts were designed to take the actual applied shear load. The design of Favelle cranes generally allows for two systems to fail prior to an event occurring. ‘In 40 years of use there has never been a position previously where three systems have failed at the one time,’ said an Australian crane engineer.
