Using their bespoke ‘cable crawler’ access gantry, Spencer Bridge Engineering installed a dehumidification system on the main cables of the Great Belt Bridge in Denmark. The system injects dry air into the cables at multiple locations, helping to slow corrosion and extend the service life of the structure. A key part of this process is the subsequent sealing of the cables to create an air-tight environment.
Spencer Bridge Engineering’s approach meant that only a single carriageway possession for the installation of its bespoke ‘cable crawler’ gantry was required. Once the gantry had been manoeuvred from the delivery vehicle to the landing trestles, the carriageway was able be re-opened with only one lane closure.
The company’s in-house development of the ‘cable crawler’ gantry for suspension bridge main cables did not only have significant positive contributions to project programme, quality and methodology, it also created opportunities to carry out other essential works without the requirement for carriageway possessions on heavily used and critical transport routes.
Throughout the project, the Spencer Bridge Engineering team and staff from Danish sub-contractor Davai, which supplies labour for specialist high-level works, walked along the cables to access Spencer Bridge Engineering’s trademarked Cable Crawler™ gantries to carry out the dehumidification works or deliver equipment and supplies.
This involved personnel walking along the cables, supported by hand ropes and wearing full body harness, for as far as 800 metres at a time, climbing for up to 190 metres at steep gradients of up to 28 degrees.
Weather was a major challenge for the project. Staff could not work from the gantries in high winds while, in wet conditions, the wrapping process could not be undertaken, nor could personnel walk on the cables.
Despite these restrictions, almost six kilometres of cables on the East Bridge were sealed in an elastomeric wrap known as Cableguard. As each section was wrapped, thermal blankets were used to heat the wrap and create a continuous airtight seal around the main cables before dry air was pumped into the lengths of wrapped cable.
The project was delivered successfully with no safety accidents or incidents, and without any disruption to the bridge’s 31,000 daily vehicle crossings, despite the challenging conditions. Any other methodology would have required full- time lane closures, carriageway possessions, multiple crane lifts and significant disruption.
