You have probably all seen the new Network Rail poster “Next Stop: Year 2186”. The first time I saw it, I was on my way to meet Mike Palmer, Network Rail’s Project Manager, responsible for the current round of engineering work on the Royal Albert Bridge. The bridge features prominently on the new poster and Mike’s project sits comfortably with the poster’s message of “Getting the Great Western Main Line ready for the next 175 years”. The fascinating project outline in this article might not extend the life expectancy of the bridge very much but it will certainly make a significant contribution.
In 1952, the bridge was pronounced a Grade 1 listed structure by English Heritage. As a consequence, Mike’s project had to undergo considerable scrutiny before approval was finally granted and every effort has been taken to maintain the original Brunel features even though some no longer contribute to the structural integrity of the bridge. The £10m project involves replacing more than 50,000 bolts, carrying out significant steelwork repairs using 100 tonnes of new steelwork, the removal of up to 46 layers of paint and then covering the bare metal with a new protective system using 36,000 litres of special paint designed for harsh marine environments.
However, before the engineering work could start, the local community had to be involved since the bridge not only straddles the River Tamar, the boundary between Devon and Cornwall, it also spans over part of the town of Saltash on the Cornish embankment. There are many homes and other buildings that sit below and around the structure and these residents are understandably, very proud of what they consider to be “their” bridge. It has formed part of their landscape for many years making a very positive contribution to their community. However, over the years and now centuries, there have been a few concerns about noise and lead pollution whenever major engineering is taking place.
To ensure that the community was fully engaged in the project two meetings were held, each one attracting more than 100 local residents. Many of the residents had previously worked on the bridge and some came with trophies and exhibits of the bridge removed by previous generations of engineers. School children were shown how the bridge worked. Metal hangers and tubes were used to mimic the bridge and the children had to guess how many bricks the structure could hold. Plenty of advice was given and this feedback heavily influenced how the work was to be staged.
Knowledge of the structure
The design work has been carried out by global consultancy company AECOM. It recently took over Faber Maunsell and has inherited its considerable knowledge of the structure represented by one of its lead designers, George Lawlor, who has carried out detailed examinations and assessments of the bridge over recent years. Taziker Industrial Ltd won the contract in what Mike described as a very competitive contest with highly innovative submissions from a number of companies. Taziker Industrial (TI) is the principal contractor on site and will be carrying out all the scaffolding, surface preparation, steelwork repairs and painting themselves using only its internal staff. TI recently carried out similar work to Weston Mill Viaduct which is situated in Plymouth, about a mile away, carrying the railway over the entrance to Devonport docks.
The project has just started and it is expected to take two years to complete. The site compound and offices are now in place on the Plymouth embankment at track level for ease of access. At present, only the approach scaffolding is in place alongside two satellite compounds situated one on each bank. All the work will take place on the two central bow arched spans. This contract does not include any ongoing work to the approach spans. The work will be carried out in five stages to ensure that the additional loading imposed on the bridge structure resulting from the scaffolding and equipment will be within acceptable loading tolerances.
HAKI scaffolding system
TI is using the HAKI scaffolding system which is not only lightweight but has unique features built into the design. The scaffold which will include a pitched roof to avoid rainwater gathering, will be encapsulated to create a contained working environment. This will reduce noise levels and ensure that polluted matter will not escape. Within this scaffold tunnel, there will be an additional tunnel around the track to allow trains to run through the work area.
On the Tamar, even on a sunny still day the airflow through the bridge structure can be considerable and very variable which means that, in very high winds, the encapsulating membrane round the scaffold can act like a sail and impose significant additional loading onto the structure. To combat this concern the HAKI system is designed so that each encapsulating membrane is retained within a vertical channel on either side. This enables it to be retracted like a “roller blind” in the event of high winds reaching a pre-determined level. The retraction can be carried out quickly and safely to minimise wind loading on the structure from the additional surface area.
The aim is to ensure that only one fifth of each span is covered at any one time. Two short sections of scaffold will be erected and encapsulated at each end of each span, making four sections. The two sections on each span will then be moved toward each other in stages as the work progresses and they will finally meet in the centre of each span to form the fifth phase.
Once each worksite is sealed, the removal of the numerous layers of paint can commence. Up to 46 layers of paint and corrosion will be grit blasted back to bare metal. This will expose the true extent of any corrosion damage and enable engineers to determine the precise remedial action necessary. It will also provide the painters with a clean surface to apply the three coat protective system, supplied by Leighs Paints which comprises a zinc primer, a glass flake epoxy intermediate coat and an impact resistant polyurethane finish coat. These will be sprayed on to the structure with hand painting in difficult areas.
The paint is expected to provide a 25-year protection to the structure which will be quite an achievement in this exposed, corrosive environment. Previous systems have only been effective for about seven years so this should offer a significant saving on future maintenance costs. The final colour selected is goose grey. The original colour of the bridge was an off white and was subsequently painted in various shades of browns, white and red until in 1911 it was painted grey and has remained that colour ever since.
Wherever possible, the grit blasting will be confined to daylight hours to minimise disturbance to the local community. Inevitably, there will be some noise when they work at track level and night time possessions are in place.
The intention is to clean the work area after each shift to remove all the grit, old lead-based paint flakes and other debris. To do this TI is installing industrial vacuum units. These units will be placed adjacent to the bridge so that the debris can be sucked out of the encapsulated working area with heavy particles going directly into vacuum skips and airborne particles into separate filtered skips ready for removal off site.
Although the bridge is considered to be in a generally good condition, a major part of the work is to carry out steelwork repairs, especially to those parts that cannot normally be reached. One key area is where the vertical hangers supporting the track deck are attached to the arched tubes at the top of the structure. The main bolts to these hanger connections are known to be corroded and the diagonal bracings are not working effectively. Whilst repairs are being carried out to one hanger connection, the adjacent connection and the two on the opposite side of the tube will be strengthened with additional bolts until the repair has been completed. This sequence will be repeated for all the hanger joints until all have been repaired.
It is interesting to note that the corroded main bolt for each joint will become redundant when the repair is complete. However, each bolt is being retained to ensure that Brunel’s original engineering thoughts, intentions and actions are retained. Another example of this commitment to heritage is at track deck level where Brunel introduced diagonal cross girders. This system enabled Brunel to use a more slender section because the axle loads would always bear on more than one girder at a time thus reducing the load on each element. These diagonal girders became redundant in the early 20th Century when new cross girders were introduced at right angles to the track, but all one hundred and seventy six will be repaired under this current programme of work.
So everything is ready. The local community will be looking on with interest. Local charities and museums are to be offered fragments of the bridge to auction or exhibit and some of the bridge metalwork no longer required will be donated to local artists and sculptures to use as they see fit. This is a thoughtful way of engaging local residents. After all, The Royal Albert Bridge is part of their community; they will be hoping that their grandchildren will be able to view this magnificent structure in 2186, as well as the trains that will hopefully still be travelling across this significant county boundary, just as they have for the last 150 years.