Protection of the East Bridge suspension cables to cost DKK 70 million

Four giant work platforms are currently being built in the UK by Spencer Group. In April, the company will begin to install a dehumidification system on the East Bridge main cables. At a cost of DKK 70 million, this will be the world’s largest project for the retrofitting of a dehumidification system.

Each platform is 33 metres long, 4.5 metres high, 3.5 metres wide and weighs 22 tonnes. This makes it 40 per cent larger and heavier than any working platform constructed previously. The cost of the design, construction and equipment amounts to a total of GBP 1 million.

The dehumidification project has been initiated to maintain the East Bridge cables in good condition. The permanent installations for the dehumidification of the main cables will counteract the risk of moisture condensation occurring in the cables over time.

“This is not because there is corrosion in the cables at the moment but, when we were about to paint the cables, we decided to install a dehumidification system instead. It is a technology that is now being integrated into many new suspension bridges and will protect the cables for the rest of their lives,” says Kim Agersø Nielsen, Technical Manager, Structures and Systems at A/S Storebælt.

The entire project will be carried out from the big four working platforms, or cable crawlers, which can move along the main cables and around the facility without disturbing the traffic during work.

“The system has many advantages. It is safe because all staff, tools and equipment are enclosed in the working platform, thus preventing loss of objects onto the roadway. The platforms move easily along the cable, without the necessity of having to dismantle anything from the bridge; also, the whole system is completely independent of traffic and allows full, continuous flow along the bridge while in operation,” says Spencer Group’s Project Director, Jim Mawson.

The working platforms are installed over night, when there is little vehicle traffic and without disrupting it, which is one of the biggest advantages of Cable Crawler system.

Work on the main cables commences in April. All access to working platforms will be from the motorway hard shoulder or the pylon top so, even if motorists do notice the work, it will not affect traffic.

The work is expected to be completed in 2015.

About the dehumidification system

The two main cables are wrapped with an airtight reinforced rubber membrane. Each cable is fitted with five injection points and eight outlet points. This makes it possible to blow dry air through the main cable from a central dehumidification system and remove any moisture in the cables.

Dehumidification systems on the main cables are integral to the majority of large suspension bridges being built today. Dehumidification of the main cables on existing bridges, for example, has been carried out on the Lillebælt Bridge, the Höga Kusten Bridge, Humber Bridge and others.

The working platforms are part of the Spencer Group “Cable Crawler System” and are the largest ever built to undertake the corrosion prevention work on suspension bridge cables. Spencer Group is based in Hull in the UK and pioneered their world-beating Cable Crawler system in 2007 when they used it to work at height to dehumidify the cables on the Forth Road Bridge in Scotland. The system has since been used to install three other dehumidification systems – on the M48 Severn Crossing and the Humber Bridge in England, as well as Älvsborg bridge in Gothenburg, Sweden.

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