Cleveland Bridge and Aecom are to undertake a 12-month inspection of the Humber Bridge.
Cleveland Bridge will act as the as principal contractor, with Aecom working as project manager.
Cleveland Bridge will examine eight panels, or sections of the main cable between hangers. In all the bridge has 120 panels, covering 18m sections of suspension cable. Four of those being inspected are at lower heights, and four at a higher level. Four panels on each cable will be inspected.
Inspectors will check the effectiveness of the dehumidification system installed to protect the cables from corrosion in 2010. Similar systems have also been installed on the Forth and Severn Road bridges.
Cleveland Bridge head of operational delivery Jim Mawson told New Civil Engineer that the lower level panels will be inspected from scaffolding, but the cable panels higher up will be inspected from two specially installed 15t bespoke gantries.
A contraflow system will be installed on the bridge to allow the gantries and scaffolding to be installed.
The first stage of the work on the cables involves removing the elastomeric wrap around the cable panel to expose the outer layer of circumferential wire, which protects the wires underneath.
This will be removed to expose wires, which are coated in a mix of lead paste and linseed oil. This protective lead paste will be removed and disposed of, as it became redundant after the dehumidifcation system was installed.
Eight wedges will then be driven into the wires in each panel to push wires apart. Once each wedge line has been opened, specialist engineers from Cowi will carry out physical inspections and remove wire samples for offsite testing.
Wire inspection on the Severn Bridge
Once all eight wedge lines have been inspected, the wires will be compacted with a bespoke hydraulic compaction machine.
Stainless steel bands will then be placed around the re-compacted wires every 300mm as the compaction machine makes its way along the 18m panel. Once this is completed, a second bespoke tool, a wire wrapper, will be brought up to the mainstay cable and used to rewrap the cables.
Finally, a highways standard paint system will be applied and covered with new elastomeric wrap over the circumferential wire.
Cleveland Bridge estimates it can complete one wedge line per day, with the cables being wrapped overnight to ensure the dehumidification system remains active during the work programme.
Once the four western panels are fully inspected, the gantries will be swapped to the eastern side of the bridge to complete the final four panels.
Winning the contract marks a return to the Humber Bridge for Cleveland Bridge as it was part of the original British Bridge Builders construction consortium, alongside Sir William Arrol & Co and Redpath Dorman Long, which built the bridge in the 1970s.
Like what you’ve read? To receive New Civil Engineer’s daily and weekly newsletters click here.