Specialist engineering contractor Spencer Group has been awarded a £3.9m contract to replace the critical components. It starts work this month.
The A-frames each weigh five tonnes and are underneath the 1,410m main span of the bridge. They have to be replaced because the A-frame bearings, which allow them to move as the bridge contracts and expands with the weather, have become worn over time.
The wear and tear has been exacerbated because of the dynamic forces on the giant structure over the 32 years since it was built, including the prevailing westerly wind blowing across the Humber estuary. Expert analysis indicated that complete replacement of the system was necessary and would provide a much improved, lower maintenance solution for the Humber Bridge Board.
Locally-based Spencer Group previously carried out a cable inspection contract on the bridge in 2009 and main cable dehumidification work to prevent corrosion in 2010.
The latest project is complex and will be carried out in cramped areas below the carriageway. Scheduled to last for a year, it will require Spencer and its subcontractors to erect scaffolding to create an expanded, uncluttered working area underneath the bridge deck before the main works can begin.
Spencer is applying a design solution developed by consulting engineer Arup.
It will involve Spencer fitting two so-called “wind shoes”, which are designed to absorb wind loading on the bridge deck and reduce the associated loads on the new bearing system.
Temporary, hydraulically-operated, load-bearing ‘arms’, designed by Spencer, will be installed to enable the A-frames to be dismantled and removed, before the permanent solution is put in place, to precision engineering standards, thereby minimising the load pressure on a critical part of the structure. Concrete strengthening work will also be carried out.
Within the project price Spencer will take the opportunity to replace four outdated, high-maintenance oil-filled transformers, which enable power and lighting systems on the bridge, with modern, air-cooled units, again to reduce maintenance costs.
Spencer project director Jim Mawson said: “The Humber Bridge is such an iconic landmark and famous world-wide, so this is very prestigious project for us, especially as the company began in Hull and we have our headquarters in the city.
“We are very proud of the fact that the Humber Bridge Board has selected us for this important project that ensures this magnificent landmark remains structurally sound for many, many generations into the future.
“This is another example of us taking on a complex and challenging job that other companies would perceive to be risky. We’ve got the people, the experience and the capability within the business to be quite comfortable with it. We’re accepting risk based on the fact that we have the team and the expertise to support this contract and meet and, indeed, exceed the client’s requirements.”
Subcontractors on the project include: ESL of Hull, which is carrying out the strip-out works; scaffolder Harsco; electrical contractor Pennine Control Systems, of Huddersfield; and steel fabricator Allerton Steel, of Northallerton.
The contract reinforces Spencer’s growing reputation for complex, high-level bridge works. It was recently appointed to carry out the largest retro-fitted bridge dehumidification project ever undertaken worldwide. The work will be carried out on the East Bridge in Denmark, the third largest suspension bridge in the world and part of the 18km Storebaelt crossing. Using its proprietary gantry system, the Cable Crawler, Spencer has carried out similar corrosion-prevention work on the Severn and Forth Road suspension bridges, and the Alvsborg Bridge in Sweden, as well as the Humber Bridge.