The ANZAC Bridge in Sydney provides a link between the central business district and the city’s western suburbs. Carrying 2 x 4 lanes, this road bridge is the longest cable-stayed bridge in Australia, with a main span of 345m. When the bridge was opened in 1995, vibrations were detected in the stay cables due to the complete lack of vibration control devices, which were not commonplace at the time. As there was a risk of the vibrations ultimately causing profound damage to the bridge, a modernisation contract was recently awarded to a consortium including Freyssinet.
Such vibrations are caused by the combined effect of wind and rain. Studies conducted by Freyssinet’s Technical Department led to the proposed solution of fitting helical contour ridges to the existing HDPE sheaths. These were fitted without any interruption to traffic using Freyssilix, a welding robot developed in partnership with Alpin Technik.
In addition to the contour ridges, which will reduce vibrations by around 80%, Freyssinet Internal Radial Dampers (IRD) will absorb any residual vibrations.
Freyssinet also designed “new generation” deviator collars for the ANZAC Bridge that increase the lever arm of the IRDs while protecting the anchorages against angular deflection.
Lastly, the Technical Department has contributed to a world first by developing and laboratory testing a ground-breaking method for replacing the filler in the stay cable anchorages. The process was verified in Australia and specifically adapted for this project. The replacement operation will start in the next few months and will significantly extend the durability of the cable-stayed structures.
A project with a focus on safety and quality
Throughout the modernisation work, the bridge’s eight lanes will remain open to traffic. To ensure the complete safety of the teams working on the bridge and for transporting materials, two 80 cm-wide fixed platforms have been fitted on either side of the bridge.
At the same time, the decision was taken to improve the permanent access systems, leading to the installation of a lift in each tower and access to all of the bridge’s deck-level anchorages.
For this entire project, Freyssinet Australia has applied the quality standards required by NSW Roads and Maritime Services. Furthermore, ever-mindful of the safety and well-being of the teams, Freyssinet Australia and its three partners have developed a comprehensive safety policy.
The project is due for completion in October 2013.
TO FIND OUT MORE:
• Maintenance of cable-stayed structures:
Please contact us if you would like to order our brochures: info@freyssinet.co.uk
FREYSSINET BEATS THE WORLD RECORD IN VLADIVOSTOK, RUSSIA, WITH A 1,104-METRE CABLE-STAYED SPAN
Designed by Russian company Mostovik, and built by Russian general contractor USK Most, who subcontracted the construction to its subsidiary SK Most and Mostovik, the Russky Island Bridge will have a total length of 1,872 metres. It is made up of a 28-metre wide central span, two A-frame towers 320 metres high, 168 parallel strand stay cables and dampers placed on each of these stay cables. Freyssinet carried out the design, production and installation of the stay cables on the structure, as well as positioning the dampers. Furthermore, Freyssinet conducted an expert appraisal on behalf of the Russian Ministry of Construction to validate the solutions selected for the design of the structure.
Compact, parallel strand stay cables to minimise the effects of the wind
For the Freyssinet team responsible for installing the stay cables and dampers, everything started in July 2011 with the positioning of the first pair of stay cables at a height of 186 metres. From that date on, the operations proceeded with the installation of the 8 planes of 21 stay cables as the bridge was built, with a total of 3,700 tonnes of strands! Due to the exceptional length of the stay cables (the longest being 582 metres, another record), Freyssinet developed individually-protected parallel strand stay cables to minimise the effects of the wind on the structure. These “compact” stay cables feature a greater number of strands, which allows the outer sheath to be saturated (approximately 20% more strands in relation to a sheath of the same diameter). The outsides of the sheaths are also fitted with helical ribs to prevent vibrations resulting from the combined effect of wind and rain. Individually anchored by wedges on upper and lower blocks arranged in the towers and in the deck, the strands and all the stay cable bridge components have a service life of 100 years.
Dampers adapted to the size of the bridge
Since 25 March and the positioning of the last stay cables, Freyssinet has been focusing on installing the dampers. These dampers, developed and patented by Freyssinet, are external for the longest stay cables and internal for the shortest ones. Furthermore, the longest stay cables installed on the central span are equipped with magnetorheological dampers, the viscosity of which is adjusted electrically in line with the vibration frequency (Maurer technology). The finishing work, which also benefits from Freyssinet innovations, is next in line.
Golden Horn, Vladivostok’s second bridge
Just 5 kilometres from the Russky Island Bridge, Freyssinet has also designed, supplied and installed 192 stay cables for the Golden Horn Bridge. Located in the heart of Vladivostok, this cable stay bridge connects the northern and southern parts of the city. With a span of 737 metres (and a total length of 1,389 metres), it will be the 10th largest cable-stayed structure in the world when it opens.