The challenge
A Grade 2 listed structure and scheduled monument, Whorlton Bridge is one of the UK’s oldest road suspension bridges, with the timber deck supported by its original iron chains. Formally opened in 1831, it was originally designed to carry horse and carts with coal from Durham coal fields.
After a routine inspection, the single file road bridge was formally closed to traffic in December 2020. Subsequent assessments concluded that the structure could not withstand the effects of load combinations for pedestrians or vehicles, with the main chains and link pins also failing under loading.
Following consent from Historic England, a programme of works commenced in early 2024, with the entire structure to be dismantled and all components to be inspected, shotblasted, tested and repainted. The parts will then be returned to their original position and as much of the original materials reused where possible.
VolkerLaser was appointed by Durham County Council to carry out the structural rehabilitation works, delivered in line with Historic England’s parameters and in coordination with the Environment Agency.
Our solution
Due to the logistical challenges the project presented, it was decided that a temporary catenary system would be installed to support the existing cables below the deck, while the entire structure was dismantled piece by piece. Designed by Case Civil & Structural Engineering, the temporary cable crane structure utilised a range of our propping equipment, including Mass 50, System 160 and Mat 125.
Speaking about the cable crane, Chris McHutchison, Senior Project Manager at VolkerLaser said “Working with Case Civil & Structural Engineering, we knew that we wanted a proprietary system that offered an adaptable, ‘off the shelf’ solution. We were attracted to Mabey Hire not only for their comprehensive and readily available product portfolio but also the detailed technical information made available. Thanks to the modular nature of the kit, we were able to easily interchange it with other systems, as well as minimise fabrication on site due to the equipment arriving ready to install.”
Formed of two pivoted towers, which stand on the north and south sides of the bridge, the temporary cable crane features five suspended catenary cables, spanning approximately 95 metres between the two towers.
Chris continued: “While this was the first time working with Mabey Hire in my current role at VolkerLaser, I have worked with them numerous times throughout my time in the industry. Whorlton Bridge is certainly a unique project and one that presented a lengthy and challenging early design process as a result of the bridge’s listed status, having to clearly demonstrate our proposed plans and gain approvals from Historic England and other parties.
“Throughout this process, the support from Mabey Hire has been fantastic. They’ve assisted us with design and technical advice, including recommendations on what equipment would be best for our requirements and working alongside our teams to gain sign-off on the proposed temporary works scheme. Mabey Hire has been brilliant throughout and helped make the process far easier.”
The cable crane was successfully installed on site in September 2024, with works to remove the timber deck, supporting beams, hangars and rods underway. The components will then be moved to a secure workshop for inspection and refurbishment.
