M5 Avonmouth Bridge
Diane Davies, with Terry Robinson, South West Engineering Team Leader, and Shane Stephens, Senior Inspection Assurance Manager, National Highways, and Paula Hewitt, Chair of the South West Infrastructure Partnership, Institution of Civil Engineers
The Avonmouth Bridge being constructed over the River Avon in the early seventies.
NATIONAL Highways is welding the future of the M5 Avonmouth Bridge for generations to come as the iconic structure marks its 50th anniversary. Over the past five decades a significant amount of unseen work has gone into maintaining the bridge and currently a programme of welding is being undertaken on the underside of the structure by the company responsible for England’s motorways and major A roads.
Work being carried out on the M5 Avonmouth Bridge.
The original six-lane bridge was designed by Freeman Fox & Partners, and with construction starting in 1969, principal contractors took five years to build and install the bridge over the River Avon near Bristol. Completion was delayed by two years following construction issues with similar box girder structures in Melbourne, Koblenz, and Milford Haven, and after further strengthening work, the bridge eventually opened for traffic on 24 May 1974.
Fifty years on, and the bridge – along with the nearby, year older Wynhol Viaduct – remains one of National Highways’ iconic structures and a gateway to the South West, carrying an average 125,000 vehicles per day.
Strengthened and widened to eight lanes between 1996 and 2001, the structure:
- Is 0.9 of a mile in total length;
- 40 metres wide;
- With a ground clearance of 30.5 metres;
- Made of reinforced concrete and steel;
- Surfaced with a denser, durable and flexible surface material (Gussasphalt); and
- Features a cycle/footpath alongside the southbound carriageway.
Funding and maintenance of the arterial structure has been the responsibility of central government and National Highways and predecessors for all of its 50 years of service, latterly in partnership with Amey.
Large water crossings such as Avonmouth, the M4 Prince of Wales Bridge and M48 Severn Bridge require specific maintenance and inspection regimes, and all three structures are now looked after by the specialist bridges inspection and maintenance (SBIM) team.
As part of a robust inspection and maintenance regime, teams have been carrying out extensive welding within the structure since October.
This includes the welding, of which most of the maintenance and renewal work goes unseen by the travelling public, taking place underneath the bridge, along the parapets and within the chambers and mezzanine flooring of the structure.
Abseiling engineers and cradle platforms have been employed as part of inspection and maintenance work, scaffold bridges are also being installed to enable safer repair work and easier access to the structure, while at the visible road level the bridge expansion joints are routinely inspected, assessed and repaired.
It is a robust inspection regime consisting of examining all bridges and other structures in line with the published guidance in the Design Manual for Roads and Bridges.
This includes general visual inspection every two years and more detailed principal inspection every six years, which identifies and records defects in reinforced concrete, steelwork and other construction materials, although structures such as the Avonmouth Bridge have more bespoke regimes, requiring a dedicated team to look after them.
Through a programme of structural inspections, investigations and assessments, substandard and potentially vulnerable structures are identified, with safeguarding measures put in place, like for the Avonmouth Bridge and Wynhol Viaduct, fully maintained for many years to come.
The Avonmouth Bridge is not only an iconic piece of infrastructure but is so important for connectivity in the South West. Looking after critical infrastructure and ensuring they meet the future needs of its region is essential.
The Avonmouth Bridge is not only an iconic piece of infrastructure but is so important for connectivity in the South West. Looking after critical infrastructure and ensuring they meet the future needs of its region is essential.
As for all infrastructure across the Strategic Road Network, the Avonmouth bridge requires plenty of TLC, and one of the main challenges is to ensure safe access for the inspection and maintenance work around this large and significant structure.
Safer and modern methods of work are continually explored, and along with gantry and runway beam studies, the use of a concrete climbing robot to potentially lessen the need for rope access was trialled.
The Avonmouth Bridge, like the M4 Prince of Wales Bridge and the M48 Severn Bridge, is a real feat of engineering, and as current custodians, there is a lot of pride taken in the work as it moves into the next 50 years of its life.
Diane Davies, with Terry Robinson, South West Engineering Team Leader, and Shane Stephens, Senior Inspection Assurance Manager, National Highways, and Paula Hewitt, Chair of the South West Infrastructure Partnership
All images courtesy of National Highways.