Bearings for dolphins

Structural spherical bearings for an industrial marine structure in Australia.

The dolphin structures that support a section of wharf of a Rio Tinto iron-ore port in western Australia are currently being replaced – with mageba structural bearings supporting the superstructure that will connect them across this harsh marine environment.

The port of Cape Lambert (Port Walcott) is used to load millions of tonnes of iron ore from the Pilbara region onto ships every week, and has two wharfs that extend far out into the ocean for the enormous tankers to dock against where the water is deep enough. The longer of these wharfs has a length of 2.7 kilometres, and it holds or shares numerous Australian bulk handling records. A section of the docking area at the outer end of the wharf is supported by a large number of dolphins – huge man-made marine structures supported on piles. The existing dolphins were determined to need replacing after twenty years of service, a testament to the wharf’s harsh marine environment.

To minimise disruption to port activities, the new dolphins are being constructed, on newly driven piles, alongside the existing structure. But this did not mean that the construction could go on unaffected by shipping; the construction work was limited to certain times of day, and by numerous other challenges arising from the project’s special needs. With a strong need to ensure reliability and flexibility in executing the project – reliability of product performance and of the delivery process, and flexibility to adapt to changing requirements – the client engaged mageba’s Australian subsidiary as its bearing supply partner. The first order of business when the project’s needs were described to our local team was to advise on the optimal choice of bearing type. Considering in particular the bearings’ installation location just above the high tide level, where they will be constantly exposed to sea spray and probably continually submerged in seawater from waves, mageba proposed the use of spherical bearings rather than pot bearings as originally anticipated by the wharf’s design. Of course, this choice of structural bearing type was also supported by an analysis of all other relevant bearing selection and design criteria – including loads, movements, rotations and the limited available space. In terms of loads, the most notable requirements were for the bearings to be designed to each resist lateral loads of 1491 kN, and also to withstand uplift forces of up to 340 kN and downward loads of up to 600 kN with frequent load reversals – with a figure of 60,000 load cycles specified for the design to ensure satisfactory long-term performance.

Following a lengthy review of this proposed change to bearing type, involving both the structural designer and the main contractor, it was finally agreed to use mageba’s tried-and-trusted RESTON®SPHERICAL bearing – 36 in total, of the fixed, free-sliding and guided-sliding types, and each designed with uplift restraints to resist the uplift forces arising. Following project-specific design by mageba and client approval of the designs, the structural bearings were manufactured in mageba’s Shanghai factory to the project’s stringent requirements, with strict quality control measures specified. In relation to the quality assurance of the steel used, mageba engaged a third-party ILAC-accredited laboratory to carry out ultrasonic testing in accordance with Australian Standard AS 1710 (Level 2) on each steel plate, and the mechanical and chemical properties of each plate were similarly tested to ensure compliance with standard AS 3678. Weekly progress reports were sent to the client throughout the production process, and upon completion of fabrication, the bearings were physically inspected and approved by the client.

For further confidence in the bearings’ design and manufacture, five of the fully manufactured structural bearings were subjected to full-scale testing as specified by the supply contract. The bearings’ special designs required some ingenuity on the part of the technicians in mageba's NATA / ILAC MRA-accredited testing laboratory in Sydney, but nothing they couldn’t overcome with the lab’s 20,000 kN test rig. The bearings were tested using a specially designed setup, with multiple tests simulating near-to-actual conditions. Following successful completion of the testing, witnessed by the client’s representative, the structural bearings were made available for collection by the client from mageba's Eastern Creek facility outside Sydney and are currently being installed. We are glad to have made a small contribution towards maximising the life expectancy of this new wharf structure, thanks to the quality and durability of our spherical bearings and the strenuous quality assurance and testing regime put in place – and hope that this will minimise future structure repair and replacement work on the wharf, benefitting not only the dolphins that inhabit the ocean along western Australis’s coast but also the area’s entire ecosystem. 

Structural designer: Aurecon
Contractor: Austral Construction Pty Ltd
Client: Rio Tinto

Aerial view of the Cape Lambert (Port Walcott) location of the wharf in question – the longest in the picture, with a length of 2.7 kilometres (© Bing Maps)

View from an access boat of the wharf structure with its docking berths for four huge iron-ore tankers at its outer end

View from below of the existing main wharf structure, high above the water, and the new structure being built at a lower level

Close-up view of the top of one new dolphin showing two bearings at one end, ready to support the superstructure that will connect it to the next dolphin

The dolphins were prefabricated before lifting into position on site – already pre-equipped with the large spherical bearings that will support the superstructure, two at each end (© Austral & RIO Tinto)

Supervision of installation of the bearings on the dolphins was provided by mageba, before the dolphins were delivered to site

Preparation of a bearing for full-scale testing at mageba’s testing laboratory near Sydney, which is certified by Australia’s National Association of Testing Authorities (NATA)