The Forth Road Bridge dehumidification project was the first time Spencer Bridge Engineering were commissioned to undertake works of this type. Using their bespoke ‘cable crawler’ access gantry, the team installed a dehumidification system on the main cables to inject dry air at multiple locations, helping slow corrosion and extend the service life of the cables.
Spencer Bridge Engineering were appointed by the Forth Estuary Transport Authority to install a dehumidification system to the main cables of the Forth Road Bridge.
The project involved the design and installation of a unique ‘cable crawler’ access gantry, which enabled the process of wrapping the main cables with an airtight membrane. This was followed by the installation of a number of inlet and outlet ports with associated piping.
Three sets of dehumidification plants were provided, one at the main mid span and one at each end of the main towers. A key part of the process was the subsequent sealing of the cables with a proprietary material to create an air-tight environment.
Significant risks associated with working at height were minimised through the use of the cable crawler gantry.
Spencer Bridge Engineering’s approach to these works required only one single carriageway possession for installation of their bespoke ‘cable crawler’ gantry. Once the gantry had been manoeuvred from the delivery vehicle to the landing trestles, the carriageway could then be re-opened with only one lane closure.
The company’s in-house development of the ‘cable crawler’ gantry for suspension bridge main cables not only had significant positive contribution 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. Any other methodology would require full-time lane closures, carriageway possessions, multiple crane lifts and significant disruption.
