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Menai Suspension Bridge works become key teaching tool for next generation of engineers

UK Highways A55 Ltd (UKH), alongside Principal Contractor Spencer Bridge Engineering (Spencer) and Principal Designer COWI, were invited to deliver a technical presentation on the hanger replacement works for the Menai Suspension Bridge to a regional meeting of the Institution of Structural Engineers on the 2nd of November 2023.

The Institution of Structural Engineers is a global membership organisation geared toward the training, assessing and development of structural engineers. The organisation acts as a platform to highlight structural projects considered as best in class and promote the sharing of expertise in this field. Using this expertise, the organisation further acts as a contributor to government policy and practices associated with the construction industry. Consisting of branches nationwide, the organisation has an active IStructE Wales Regional Group, which focuses on enhancing the best skills to be used on new and innovative development projects across Wales.

Spencer specialises in the design, construction, and maintenance of complex and unique structures and have completed notable projects around the world such as restoration works on the Union Chain Bridge joining England to Scotland, and delivering the world’s largest retrofit cable dehumidification project on Denmark’s vast Great Belt crossing

COWI is established internationally as a bridge engineering consultant, with designs such as the 1915 Canakkale Bridge (currently the longest in the world) in its portfolio. Within the UK, COWI led the design joint venture for the Mersey Gateway Bridge. COWI often works on heritage and listed bridges, advising owners and operators. 

UKH initially appointed Spencer and COWI to investigate the condition of the approach hangers on the Menai Suspension Bridge in 2021, both COWI and Spencer’s were at the forefront of the emergency programme of works to allow the Menai Suspension Bridge to re-open with a 7.5 tonne weight restriction in February (phase one). Both firms are now working on the permanent works phase (phase two) on the Menai Suspension Bridge

A key design constraint during phase one was that the fail-safes must permit the replacement of the existing hangers during the second phase of works later in the year without needing to be removed. The design was developed at pace following the unexpected closure and involved very close collaboration between all parties to understand the constraints and interface between the temporary works and the bridge.

At the same time, UKH, Spencer, and COWI continued to work together to develop a second phase works programme to enable the bridge to reopen without any restrictions. The second phase removes 168 existing hangers using a custom designed de-tensioning rig and replaces them with new hangers. The de-tensioning rig is installed inside the fail-safe mechanisms from the first phase of works, which are kept in place throughout the programme for safety.

On a technical level, the team were able to reroute the load path of the current hangers using cleverly designed secondary fail-safe mechanisms without removing the hangers. This ingenuity made the bridge safe to remain open to the public and safe to hold the weight of the bridge and vehicles whilst the permanent works take place.

Operationally, disruption to traffic flow between the Isle of Anglesey and the mainland has been kept to a minimum, and traffic management operators have been able to swiftly react to any sudden changes or network requirements.

Throughout all phases of work Spencer and COWI, in collaboration with the Welsh Government and UKH, have considered various options for a solution, taking into account availability of components and how quickly any bespoke items could be manufactured. 

It is expected that all required works will be completed by the end of August 2025 (subject to weather). This will ensure the Menai Suspension Bridge is ready for its 200th anniversary in 2026.

Luke Fisher, Bridges Director at Spencer Bridge Engineering said, ”We’re really proud of what we achieved for the emergency works last year. To reopen a bridge in such a short space of time following immediate unplanned closure, is not something you see very often on historic and complex structures like the Menai Suspension Bridge. This was only made possible by the incredible efforts of the whole project team and stakeholders.”

John Rees, Director of COWI’s UK Bridge Division said, ”It was a pleasure to replay the story of the Menai Suspension Bridge emergency works to an engaged and interested audience, and reminded all three presenters of what can be achieved when like-minds collaborate to solve a safety critical issue.”

A spokesperson for UK Highways A55 Ltd said, “It is a testament to the professionalism and technical excellence of the entire Menai Suspension Bridge emergency works team that this project was delivered in record time to ensure minimal disruption to the communities that rely on the bridge in north west Wales.”

The Menai Suspension Bridge presentation at the Institution for Structural Engineers focussed on both the technical and operational aspects of the phase one emergency works and second phase permanent works. The engineers delivering the talk provided valuable insight not only into the thought leadership necessary to find solutions to unique cases, but also on how to manage such projects alongside stakeholders and the local community. The presentation on work completed on this historic bridge aimed to inspire the next generation of engineers.