PRINCIPAL BRIDGE INSPECTION CASE STUDY

PROJECT: PRINCIPAL BRIDGE INSPECTION

CLIENT: MOTT MACDONALD

LOCATION: MENAI BRIDGE

In July 2009 Vertical Access Ltd were appointed as Subconsultant to Mott Macdonald to undertake the Principal Bridge Inspection of the Menai Bridge.

Thomas Telford’s Menai Suspension Bridge,
which is a Grade 1 listed structure, crosses the
Menai Strait at its narrowest point near the village
of Porthaethwy (Menai Bridge).

The bridge was originally constructed in 1826 with iron suspension chains carrying a wooden deck.
In 1940 the entire super-structure and suspension chains were replaced, however, the original masonry works to the towers and approach remains unchanged.

This inspection was carried out in July 2009, during which the masonry structure, chains, trusses, hangers and traverse cross members were inspected. The bridge masters house or toll house was also inspected in conjunction with the suspension chains.

The bridge consists of a centrally suspended span with masonry arch approach viaducts at each end. The main support towers rise 52m above the low water mark, 17m above the roadway and are 176.75m apart.

Traffic management was utilised during the night time road closures for the inspection of the chains, suspension cables and related elements, and the above carriageway elevations of the towers.

The Principal Inspection was based on a close visual inspection to standard BD 63/93. Operatives gained access to within touching distance of all inspectable elements in accordance with direction from Mott MacDonald. All elements were classified in accordance with Form BE 11/94 of BA 63/94.

Access to the masonry piers and deck soffit was gained utilising Industrial Rope Access. The suspension chains and associated elements were inspected utilising Mobile Elevated Work Platforms [ MEWP ] during the night time road closure