Written question WQ86591

The brittle nature of the components of the hangers was initially identified in reports in the 1990s, pre-devolution. At that time, the hangers were analysed by Sir Alexander Gibb and Partners. A number of the hangers were replaced with hangers made from more ductile materials.

In the 1990s, the bridge was assessed as being suitable for use at 40t. Since the 1990’s regular inspections have taken place by UK Highways A55 Ltd, the Design, Build, Finance and Operator (DBFO) of the A5 Menai Suspension Bridge. This inspection regime included General Inspections every 2 years and Principal Inspections every 10 years. The inspections have not shown any issues with the hangers until 2019 during a Principal Inspection and repainting of the hangers as a medium priority measure was identified.

However, the more recent structural analysis COWI undertook in October, which led to the emergency closure of the bridge, demonstrated that in certain loading conditions, when the bridge could be subjected to shock loading, such as harsh braking, could lead to a catastrophic failure of the suspended bridge deck.

Shock loading, while being an extremely low-risk likelihood, could lead to a brittle failure of the hangers and through load transfer to adjacent hangers – an “unzipping” effect on the suspended bridge deck – leading to a catastrophic failure.