Compare the engineering of tower cranes, mobile cranes and ship-to-shore container cranes, identify the structural and mechanical engineering principles in each, and apply this to Australian construction and port case studies

What this dot point is asking

NESA wants you to compare the engineering of three classes of crane (tower, mobile, ship-to-shore container), identify the structural and mechanical engineering decisions that distinguish them, and link the engineering to Australian sites where each is used in practice.

The answer

Tower cranes

A tower crane consists of:

• Foundation. A reinforced concrete pad or a free-standing climbing base.
• Mast. Bolted or pinned lattice steel sections, typically 1.6 m square in section, climbed by hydraulic jacks as the building rises.
• Slewing ring. A large diameter bearing ring with internal teeth, driven by a slewing motor and gearbox at the top of the mast.
• Working jib. Forward horizontal jib with the trolley and hoist rope.
• Counter jib. Rear jib carrying the hoist machinery and concrete ballast blocks for balance.
• Hoist drive. A 30 to 110 kW three-phase induction motor with VSD, driving a winch drum through a planetary gearbox.

Capacity is given as a load chart: maximum load at minimum and maximum radius. A typical city tower crane lifts 1.5 tonnes at 60 m radius and 12 tonnes at 13 m radius. The capacity falls with radius because the moment about the slewing ring is the constraint.

Australian use. Tower cranes are visible on most Sydney CBD and Parramatta high-rise sites. Operators are licensed by SafeWork NSW (CN class). Operators do not stand on the load; they sit in a cab 80 to 150 m above the street and communicate by radio to dogmen on the deck.

Mobile cranes

A mobile crane has a wheeled or tracked carrier with a telescoping or lattice boom. Categories:

• All-terrain crane. Multi-axle wheeled carrier (4 to 9 axles) with road-legal speed, hydraulic outrigger stabilisers, and telescoping boom 30 to 100 m long. Lifts 50 to 700 tonnes.
• Crawler crane. Tracked carrier (cannot travel on roads), lattice boom, very high capacity (300 to 3000 tonnes). Used in wind-turbine installation and major bridge erection.
• Truck-mounted crane. Smaller, road-going on a flatbed truck, capacity 5 to 30 tonnes. Common on building-supply deliveries.

Mobile cranes use hydraulic cylinders (Pascal's principle) for the telescoping boom and the outriggers, and wire rope drums for the main hoist. The operator's manual is the load chart, which depends on boom length, boom angle, outrigger spread, and counterweight configuration.

Australian use. Major all-terrain cranes by Liebherr (LTM 1750), Tadano and Demag. Construction companies including Boom Logistics, Sven Construction, and Lendlease operate fleets. The Sydney Metro tunnel boring machine launch and recovery operations used some of the largest mobile cranes ever assembled in Australia.

Ship-to-shore container cranes

Port Botany and the Port of Melbourne use ship-to-shore cranes that gantry along the wharf on rails. Key engineering features:

• A-frame or single-leg structure. Welded steel box sections, 60 to 90 m tall, designed to AS4100 for combined gravity, wind and seismic loads.
• Boom. Cantilevers over the ship for the full beam (up to 65 m for new generation cranes). Hinged at the inboard end to fold up when not in use.
• Trolley. Travels along the boom on rails, with a hoist that lowers a spreader bar onto the top corner castings of a container.
• Spreader bar. Adjustable to ISO 20-foot, 40-foot, 45-foot or twin-20 container lifts. Lifts up to 65 tonnes.
• Hoist drive. 600 to 1200 kW three-phase synchronous or induction motors with VSDs. Hoist speeds 90 to 180 m/min at full load, up to 240 m/min empty.
• Trolley drive. 300 to 600 kW drives, with travel speeds up to 250 m/min.

Australian use. Port Botany has terminals operated by DP World, Patrick AutoStrad and Hutchison. The Patrick AutoStrad terminal uses fully automated ship-to-shore cranes coordinated with automated straddle carriers on the yard. Crane manufacturers include ZPMC (Shanghai), Konecranes (Finland) and Liebherr.

Common engineering principles

All three crane types share:

• Structural steel mainframe designed to AS4100.
• Hoist powered by an electric motor (DC for older cranes, induction or synchronous AC with VSD for modern).
• Wire rope rated to AS2759 with a factor of safety from AS1418 (5 for general crane hoists).
• Load limiting and overload-protection systems that prevent the operator from exceeding the load chart.
• Wind speed alarms and lockouts (typical limit 72 km/h for tower cranes in service).

Where they differ