News update from the construction side of things
https://www.pbctoday.co.uk/news/plannin ... ion/84933/
Barmouth bridge
Moderators: Bearbonesnorm, Taylor, Chew
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JohnClimber
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Bearbonesnorm
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Re: Barmouth bridge
That's very good news considering its entire future was in the balance not long since. 
May the bridges you burn light your way
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JohnClimber
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Re: Barmouth bridge
Hope it's open for someone's January Winter EventBearbonesnorm wrote: ↑Tue Nov 10, 2020 4:18 pm That's very good news considering its entire future was in the balance not long since.
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RIP
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Re: Barmouth bridge
JohnClimber wrote: ↑Tue Nov 10, 2020 4:39 pmHope it's open for someone's January Winter EventBearbonesnorm wrote: ↑Tue Nov 10, 2020 4:18 pm That's very good news considering its entire future was in the balance not long since.
Have to tempt the ferryman out of Davy Jones Locker with a suitable offer for a one-off crossing...
"My God, Ponsonby, I'm two-thirds of the way to the grave and what have I done?" - RIP
The sign outside the asylum is the wrong way round.....
"At least you got some stories" - James Acaster
The sign outside the asylum is the wrong way round.....
"At least you got some stories" - James Acaster
Re: Barmouth bridge
That brings back memories, I lived on the south end of that bridge in the mid/late 80s.
Sounds a bit like Trigger’s broom
Sounds a bit like Trigger’s broom
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In Reverse
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Re: Barmouth bridge
Bit more on this for those interested from one of the trade rags
Future of Bridges | Network Rail breathes new life into Barmouth’s timber viaduct
Network Rail is giving its 154 year old Barmouth Viaduct a much needed new lease of life, while ensuring its iconic heritage is preserved.
Network Rail looks after 30,000 structures. Only nine are timber bridges. Arguably the most iconic of those nine is the Barmouth Viaduct, but at 154 years old it was rotting from the inside out just a few years ago.
Network Rail and its main contractor Alun Griffiths is now two years into a £30M restoration project and has just begun the third and final phase of work. The scheme is scheduled to be complete by autumn 2023. This work should safeguard the structure for up to 60 years with Network Rail expecting it to be another 20 years before another phase of major maintenance is needed.
The single-track timber railway viaduct, constructed by the Aberystwyth & Welsh Coast Railway in the 1860s, crosses the Afon Mawddach estuary from north to south near Barmouth in Wales. As well as the railway, the bridge carries a pedestrian and cycle pathway owned by Gwynedd County Council.
The bridge is the UK’s longest and oldest timber viaduct, stretching 820m. It is made up of 117 spans, each between 5.8m to 6.2m long. Timber forms 113 of the spans and there are four steel spans at the north end.
The structure was converted into a swing bridge in the early 1900s. Originally the bridge included a lift span to allow tall ships to pass through. This was replaced by a 41.5m steel swing span carried on cast iron cylinders in the early 1900s although has not been functional since it was closed in the 1980s.
As part of the restoration project, the swing span will retain the existing slew ring and mechanical equipment, but purely for aesthetic reasons. It is part of an agreement with Cadw – the historic environment service of the Welsh Government – relating to the bridge’s Grade II* listed status.
The bridge’s listed status means that Network Rail and Alun Griffiths are working hard to maintain the viaduct’s appearance by replacing the timber and metallic elements on a like-for-like basis. Other elements will also be retained or added for heritage reasons. These include hundreds of “fake rivets” that have been added to the structure to match the bridge’s “original identity”. “The rivets don’t do anything,” Network Rail project manager Gareth Yates adds. “They are purely aesthetic but their retainment is part of the requirements of the job and rightly so, in my opinion. The bridge is steeped in history and we are proud to be maintaining that history.”
During the first two phases Network Rail and Alun Griffiths focused largely on replacing and repairing the decayed timber elements of the bridge. In total, engineers replaced 53 of the 565 timber piles, 119 of 226 diagonal timbers and 102 of 226 horizontal support walings.
Concrete shrouds around the bases of the piles have been replaced on 109 piles, while a further 70 shrouds have been repaired.
All main rail supporting timber has also been replaced. This includes 226 corbels – short timbers which sit on the crosshead beams to support the deck beams – and 456 deck beam sections. All 226 longitudinal timbers have also been replaced as well as 81 crosshead beams.
Also replaced was the walkway decking while 660m of existing bullhead rail was replaced by more modern flat bottom rail which will help reduce future maintenance.
Timber damage
Greenheart hardwood from Guyana has been used in place of the old, decayed timber which was largely Douglas fir and Pitch pine. Greenheart hardwood is the most durable timber for marine works and is resistant to teredo worm attacks, which closed the bridge for six months in the 1980s.
That closure also resulted in the replacement of 50 piles and the encasement of pile bases in concrete shrouds.
Access to the whole structure from below was only possible at low spring tide
This time, however, the timber work was badly affected by water which had seeped into gaps between interfacing timbers. Alun Griffiths operations manager Steve Richardson explains that from initial visual inspections, the “bridge looked in fairly good order”. However, the true extent of the damage was revealed when inspecting the timber interfaces.
“The real problems we ran into were in the interfaces between timbers, where you have two beams against each other,” Richardson says. “From the outside the bridge looked ok. But when we separated beams from one another it was a different story. In several cases, water had got in between the beams and some of them were in such a bad way that we had no other choice but to replace them straight away.
“Not everything needed replacing immediately, but it would have done in a few years’ time. What Network Rail decided to do, which I think was a fantastic call, was to make the decision to replace all the rail carrying timbers in one go which allowed much better alignment of track. That way you also start the clock on the bridge’s lifecycle at the same time. If we’d have replaced the worst timber elements and left others that weren’t so bad we’d have had to keep coming back to carry out work. Now we know that there should be no need for intervention in the next 20 years and the viaduct itself will have a 40 to 60 year lifespan.”
As more elements of the bridge were removed it was discovered that most of the existing piles were defective. Eighty percent of them had split at the top as a result of rust jacking of the bolts which connect the piles to the crossheads via a steel strap. It was also discovered that the existing crossheads had rotated, resulting in pinch points where the beams and corbels landed, rather than the required bearing area between the two surfaces.
To overcome this, Alun Griffiths and timber repair specialists Trac Structural jointly developed an epoxy resin system which was injected at high pressure to fill all voids down to 0.2mm, resulting in a 100% bearing area being achieved at each interface.
Overcoming challenges
The unique location and nature of the bridge also meant that a bespoke methodology had to be developed to overcome the engineering and environmental challenges. The main driver was to minimise tidal dependent critical path works.
Working from the beach meant that access to the entire structure was only possible during low spring tides – which significantly limited the amount of time available to work on the bridge. Instead, the decision was taken to work from the viaduct itself.
During a three month blockade of the railway, two 44t road rail cranes worked from the centre of the bridge, starting at span 57, and making their way towards the respective banks of the estuary.
First the cranes removed the track before removing the timber sections, most of which were passed to support road rail vehicles and take off the structure. The crossheads were removed and lowered onto a pontoon below. After the old timber sections had been removed, the new timbers were brought to site by rail trailers from compounds on either side of the estuary.
Positioning the crane in the last span with an open span immediately in front of it had never been done on a timber structure in the UK and there were concerns that the bridge would fail under the weight of the cranes. To overcome this Alun Griffiths assembled full mock-up spans and carried out load testing for actual lifting operations.
The main challenge was the weather. In agreement with Gwynedd County Council and Transport for Wales, which operates the railway, all work had to be completed outside tourism seasons.
As such, the majority of the work has been done during the winter and autumn months.
“Tourism is a massive part of the economy in this part of the world so we agreed not to work during the summer months,” Yates says.
“The downside is we’ve had to work through some pretty horrendous conditions. There have been times where we’ve had rain going sidewards and 96km/h winds battering us from all angles – there have been days where we’ve not allowed anyone to go out on to the bridge as the conditions were simply not safe.”
He adds: “At the time, when you’re working out in the cold and rain it’s not very enjoyable. But looking back now it is a huge honour to work on such an iconic structure – it’s the kind of thing some engineers wait their whole life for.”
Final phase
The final phase of work focuses on restoring the metal elements of the bridge. Originally planned to take place in one go this autumn, the job has been split across the next two years to reduce the impact on rail services and tourism.
As well as upgrading the metal elements of the bridge, additional repairs will include strengthening work to the north abutments and further upgrades of some of the timber elements.
The steel cylinder substructures supporting the swing span will be grit blasted, repaired and painted. New 40m long steel girders for the swing span will then be installed with a temporary gantry structure erected to support the old structure as it is dismantled and lowered onto pontoons on the river. The new girders will then be jacked horizontally into their final locations and cross girders and decking will be lifted from pontoons. Finally, the temporary gantry will be dismantled and removed.
Dates for working on the viaduct during 2023 are still being finalised, but all things being well the iconic Barmouth Viaduct should be fully restored to its former glory by this time next year.
Future of Bridges | Network Rail breathes new life into Barmouth’s timber viaduct
Network Rail is giving its 154 year old Barmouth Viaduct a much needed new lease of life, while ensuring its iconic heritage is preserved.
Network Rail looks after 30,000 structures. Only nine are timber bridges. Arguably the most iconic of those nine is the Barmouth Viaduct, but at 154 years old it was rotting from the inside out just a few years ago.
Network Rail and its main contractor Alun Griffiths is now two years into a £30M restoration project and has just begun the third and final phase of work. The scheme is scheduled to be complete by autumn 2023. This work should safeguard the structure for up to 60 years with Network Rail expecting it to be another 20 years before another phase of major maintenance is needed.
The single-track timber railway viaduct, constructed by the Aberystwyth & Welsh Coast Railway in the 1860s, crosses the Afon Mawddach estuary from north to south near Barmouth in Wales. As well as the railway, the bridge carries a pedestrian and cycle pathway owned by Gwynedd County Council.
The bridge is the UK’s longest and oldest timber viaduct, stretching 820m. It is made up of 117 spans, each between 5.8m to 6.2m long. Timber forms 113 of the spans and there are four steel spans at the north end.
The structure was converted into a swing bridge in the early 1900s. Originally the bridge included a lift span to allow tall ships to pass through. This was replaced by a 41.5m steel swing span carried on cast iron cylinders in the early 1900s although has not been functional since it was closed in the 1980s.
As part of the restoration project, the swing span will retain the existing slew ring and mechanical equipment, but purely for aesthetic reasons. It is part of an agreement with Cadw – the historic environment service of the Welsh Government – relating to the bridge’s Grade II* listed status.
The bridge’s listed status means that Network Rail and Alun Griffiths are working hard to maintain the viaduct’s appearance by replacing the timber and metallic elements on a like-for-like basis. Other elements will also be retained or added for heritage reasons. These include hundreds of “fake rivets” that have been added to the structure to match the bridge’s “original identity”. “The rivets don’t do anything,” Network Rail project manager Gareth Yates adds. “They are purely aesthetic but their retainment is part of the requirements of the job and rightly so, in my opinion. The bridge is steeped in history and we are proud to be maintaining that history.”
During the first two phases Network Rail and Alun Griffiths focused largely on replacing and repairing the decayed timber elements of the bridge. In total, engineers replaced 53 of the 565 timber piles, 119 of 226 diagonal timbers and 102 of 226 horizontal support walings.
Concrete shrouds around the bases of the piles have been replaced on 109 piles, while a further 70 shrouds have been repaired.
All main rail supporting timber has also been replaced. This includes 226 corbels – short timbers which sit on the crosshead beams to support the deck beams – and 456 deck beam sections. All 226 longitudinal timbers have also been replaced as well as 81 crosshead beams.
Also replaced was the walkway decking while 660m of existing bullhead rail was replaced by more modern flat bottom rail which will help reduce future maintenance.
Timber damage
Greenheart hardwood from Guyana has been used in place of the old, decayed timber which was largely Douglas fir and Pitch pine. Greenheart hardwood is the most durable timber for marine works and is resistant to teredo worm attacks, which closed the bridge for six months in the 1980s.
That closure also resulted in the replacement of 50 piles and the encasement of pile bases in concrete shrouds.
Access to the whole structure from below was only possible at low spring tide
This time, however, the timber work was badly affected by water which had seeped into gaps between interfacing timbers. Alun Griffiths operations manager Steve Richardson explains that from initial visual inspections, the “bridge looked in fairly good order”. However, the true extent of the damage was revealed when inspecting the timber interfaces.
“The real problems we ran into were in the interfaces between timbers, where you have two beams against each other,” Richardson says. “From the outside the bridge looked ok. But when we separated beams from one another it was a different story. In several cases, water had got in between the beams and some of them were in such a bad way that we had no other choice but to replace them straight away.
“Not everything needed replacing immediately, but it would have done in a few years’ time. What Network Rail decided to do, which I think was a fantastic call, was to make the decision to replace all the rail carrying timbers in one go which allowed much better alignment of track. That way you also start the clock on the bridge’s lifecycle at the same time. If we’d have replaced the worst timber elements and left others that weren’t so bad we’d have had to keep coming back to carry out work. Now we know that there should be no need for intervention in the next 20 years and the viaduct itself will have a 40 to 60 year lifespan.”
As more elements of the bridge were removed it was discovered that most of the existing piles were defective. Eighty percent of them had split at the top as a result of rust jacking of the bolts which connect the piles to the crossheads via a steel strap. It was also discovered that the existing crossheads had rotated, resulting in pinch points where the beams and corbels landed, rather than the required bearing area between the two surfaces.
To overcome this, Alun Griffiths and timber repair specialists Trac Structural jointly developed an epoxy resin system which was injected at high pressure to fill all voids down to 0.2mm, resulting in a 100% bearing area being achieved at each interface.
Overcoming challenges
The unique location and nature of the bridge also meant that a bespoke methodology had to be developed to overcome the engineering and environmental challenges. The main driver was to minimise tidal dependent critical path works.
Working from the beach meant that access to the entire structure was only possible during low spring tides – which significantly limited the amount of time available to work on the bridge. Instead, the decision was taken to work from the viaduct itself.
During a three month blockade of the railway, two 44t road rail cranes worked from the centre of the bridge, starting at span 57, and making their way towards the respective banks of the estuary.
First the cranes removed the track before removing the timber sections, most of which were passed to support road rail vehicles and take off the structure. The crossheads were removed and lowered onto a pontoon below. After the old timber sections had been removed, the new timbers were brought to site by rail trailers from compounds on either side of the estuary.
Positioning the crane in the last span with an open span immediately in front of it had never been done on a timber structure in the UK and there were concerns that the bridge would fail under the weight of the cranes. To overcome this Alun Griffiths assembled full mock-up spans and carried out load testing for actual lifting operations.
The main challenge was the weather. In agreement with Gwynedd County Council and Transport for Wales, which operates the railway, all work had to be completed outside tourism seasons.
As such, the majority of the work has been done during the winter and autumn months.
“Tourism is a massive part of the economy in this part of the world so we agreed not to work during the summer months,” Yates says.
“The downside is we’ve had to work through some pretty horrendous conditions. There have been times where we’ve had rain going sidewards and 96km/h winds battering us from all angles – there have been days where we’ve not allowed anyone to go out on to the bridge as the conditions were simply not safe.”
He adds: “At the time, when you’re working out in the cold and rain it’s not very enjoyable. But looking back now it is a huge honour to work on such an iconic structure – it’s the kind of thing some engineers wait their whole life for.”
Final phase
The final phase of work focuses on restoring the metal elements of the bridge. Originally planned to take place in one go this autumn, the job has been split across the next two years to reduce the impact on rail services and tourism.
As well as upgrading the metal elements of the bridge, additional repairs will include strengthening work to the north abutments and further upgrades of some of the timber elements.
The steel cylinder substructures supporting the swing span will be grit blasted, repaired and painted. New 40m long steel girders for the swing span will then be installed with a temporary gantry structure erected to support the old structure as it is dismantled and lowered onto pontoons on the river. The new girders will then be jacked horizontally into their final locations and cross girders and decking will be lifted from pontoons. Finally, the temporary gantry will be dismantled and removed.
Dates for working on the viaduct during 2023 are still being finalised, but all things being well the iconic Barmouth Viaduct should be fully restored to its former glory by this time next year.
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RIP
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Re: Barmouth bridge
Thanks Andy, an interesting read.
So here they're fortifying the structure against the encroaching sea, but just down the road they're going to abandon a whole village to that same sea....
So here they're fortifying the structure against the encroaching sea, but just down the road they're going to abandon a whole village to that same sea....
"My God, Ponsonby, I'm two-thirds of the way to the grave and what have I done?" - RIP
The sign outside the asylum is the wrong way round.....
"At least you got some stories" - James Acaster
The sign outside the asylum is the wrong way round.....
"At least you got some stories" - James Acaster
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Bearbonesnorm
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Re: Barmouth bridge
I do like a bit of Green Heart. Makes a lovely bow wood but not easy to come across ... maybe I need to pay a visit one (dark) evening.
May the bridges you burn light your way
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RIP
- Posts: 9058
- Joined: Wed Nov 12, 2014 7:24 pm
- Location: Surfing The Shores Of Sanity Since 1959
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Re: Barmouth bridge
Train every couple of hours each way, strikes permitting, how fast can you cut....
"My God, Ponsonby, I'm two-thirds of the way to the grave and what have I done?" - RIP
The sign outside the asylum is the wrong way round.....
"At least you got some stories" - James Acaster
The sign outside the asylum is the wrong way round.....
"At least you got some stories" - James Acaster