How prone are the two Severn Bridges to swaying?

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Re: How prone are the two Severn Bridges to swaying?

Post by KeithW »

RJDG14 wrote: Sun Jul 31, 2022 16:18 The Forth Rail Bridge looks pretty well designed for a railway bridge from the 19th Century. The original Tay Bridge looks pretty flimsy by modern standards with little to no high wind support. The original Tacoma Narrows Bridge looked fairly well designed for its day in terms of its suspension and towers but from the pictures and opening booklet that I can find, the main deck looked very basic with virtually no regard made for airflow underneath.
The original Tay Bridge was made of cast iron which is prone to failure at the best of times but as the enquiry after the fact stated the bridge had been "badly designed, badly built, and badly maintained".

Badly designed as Bouch had not made an adequate allowance for wind loading.

Badly built as the cast iron columns were not made by the iron works he has used previously and proved to be of poor quality. So bad were they that holes in the side of the column were filled with a mixture of beeswax, iron filings and rosin.

Badly maintained as the horizontal tie bars had not been properly tightened and this meant the trains would sway as they crossed the bridge.

The final blow was that on the night in question the cross wind was very high making the train sway as it crossed, its believed that the locomotive struck one of the cross members which caused a massive structural failure, it also seems to have been exceeding the bridge speed limit.

The result so damaged public faith that the Forth Bridge was massively overdesigned. As part of the final testing Two trains, each consisting of three heavy locomotives and 50 wagons loaded with coal, totalling 1,880 tons in weight, were driven slowly from South Queensferry to the middle of the north cantilever, stopping frequently to measure the deflection of the bridge. This represented more than twice the design load of the bridge: the deflection under load was as expected.

As for the Tacoma Narrows bridge when it was designed it was not normal practise for bridge designers to take the aerodynamics of the bridge into account. In the case of a massive steel structure such as the Forth Rail bridge this simply was not an issue. Do remember that both the original Severn and Forth road bridges have been found to have problems of their own, mainly to do with corrosion inside the suspension cables and attachment points.
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Re: How prone are the two Severn Bridges to swaying?

Post by linuxrocks »

The Bridge Designer allows you to model diferent designs and see which is the most effective. The students at the last school I work at, used to see how much flex they could get in a bridge, before is collapsed.
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Re: How prone are the two Severn Bridges to swaying?

Post by RJDG14 »

linuxrocks wrote: Mon Aug 01, 2022 12:46 The Bridge Designer allows you to model diferent designs and see which is the most effective. The students at the last school I work at, used to see how much flex they could get in a bridge, before is collapsed.
This might be quite fun for me to try out, especially since it's free. Thanks for sharing!
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Re: How prone are the two Severn Bridges to swaying?

Post by KeithW »

linuxrocks wrote: Mon Aug 01, 2022 12:46 The Bridge Designer allows you to model diferent designs and see which is the most effective. The students at the last school I work at, used to see how much flex they could get in a bridge, before is collapsed.
One of the first railway bridges built was across the Tees for the Stockton and Darlington railway, the first iteration was an unstiffened suspension bridge which sagged so much that a replacement built using wrought iron girders was built. The original bridge did survive for some years but the weight of trains that used it was dramatically reduced

Image

This is the latest replacement.

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Re: How prone are the two Severn Bridges to swaying?

Post by skiddaw05 »

KeithW wrote: Mon Aug 01, 2022 13:14
linuxrocks wrote: Mon Aug 01, 2022 12:46 The Bridge Designer allows you to model diferent designs and see which is the most effective. The students at the last school I work at, used to see how much flex they could get in a bridge, before is collapsed.
One of the first railway bridges built was across the Tees for the Stockton and Darlington railway, the first iteration was an unstiffened suspension bridge which sagged so much that a replacement built using wrought iron girders was built. The original bridge did survive for some years but the weight of trains that used it was dramatically reduced

Image

This is the latest replacement.

Image
Couldn't they have attempted to make it even remotely attractive?
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Re: How prone are the two Severn Bridges to swaying?

Post by Bryn666 »

skiddaw05 wrote: Mon Aug 01, 2022 13:28
KeithW wrote: Mon Aug 01, 2022 13:14
linuxrocks wrote: Mon Aug 01, 2022 12:46 The Bridge Designer allows you to model diferent designs and see which is the most effective. The students at the last school I work at, used to see how much flex they could get in a bridge, before is collapsed.
One of the first railway bridges built was across the Tees for the Stockton and Darlington railway, the first iteration was an unstiffened suspension bridge which sagged so much that a replacement built using wrought iron girders was built. The original bridge did survive for some years but the weight of trains that used it was dramatically reduced

Image

This is the latest replacement.

Image
Couldn't they have attempted to make it even remotely attractive?
Aesthetics cost money and politicians at the Treasury don't put that into their spreadsheets.
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Re: How prone are the two Severn Bridges to swaying?

Post by RJDG14 »

Bryn666 wrote: Mon Aug 01, 2022 13:43
skiddaw05 wrote: Mon Aug 01, 2022 13:28
KeithW wrote: Mon Aug 01, 2022 13:14

One of the first railway bridges built was across the Tees for the Stockton and Darlington railway, the first iteration was an unstiffened suspension bridge which sagged so much that a replacement built using wrought iron girders was built. The original bridge did survive for some years but the weight of trains that used it was dramatically reduced

Image

This is the latest replacement.

Image
Couldn't they have attempted to make it even remotely attractive?
Aesthetics cost money and politicians at the Treasury don't put that into their spreadsheets.
The design of that 19th Century bridge looks fine as a footbridge or maybe even a low-traffic bridge for low weight vehicles (cars and motorcycles) but I wouldn't want to drive a HGV yet alone a train across it.
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Re: How prone are the two Severn Bridges to swaying?

Post by KeithW »

RJDG14 wrote: Mon Aug 01, 2022 13:49 The design of that 19th Century bridge looks fine as a footbridge or maybe even a low-traffic bridge for low weight vehicles (cars and motorcycles) but I wouldn't want to drive a HGV yet alone a train across it.
It carried heavy traffic for over 100 years and the piers were built in 1846 and it was only replaced as the embankment was no longer able to carry the increasing load.

This is the sort of train it was designed for.
Image

At the end it could carry trains like this

Image
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Re: How prone are the two Severn Bridges to swaying?

Post by RJDG14 »

KeithW wrote: Mon Aug 01, 2022 14:39
RJDG14 wrote: Mon Aug 01, 2022 13:49 The design of that 19th Century bridge looks fine as a footbridge or maybe even a low-traffic bridge for low weight vehicles (cars and motorcycles) but I wouldn't want to drive a HGV yet alone a train across it.
It carried heavy traffic for over 100 years and the piers were built in 1846 and it was only replaced as the embankment was no longer able to carry the increasing load.

This is the sort of train it was designed for.
Image

At the end it could carry trains like this

Image
I meant the 19th Century suspension bridge, not the newer looking bridge on the right that was also likely from the 19th Century.
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Re: How prone are the two Severn Bridges to swaying?

Post by KeithW »

RJDG14 wrote: Mon Aug 01, 2022 14:44 I meant the 19th Century suspension bridge, not the newer looking bridge on the right that was also likely from the 19th Century.

That one is positively modern :)

The sequence goes like this

1) 1830 the suspension bridge.
2) The 1844 Stockton Railway Bridge designed and built by Robert Stephenson
3) The 1881 bridge which had the track lifted but existed until 2008.
Image
4) The 1906 bridge built of steel on the masonry piers of the 1844 bridge
5) The modern bridge built on the site of the the 1881 bridge which was demolished to make way for it.

The big talking point in these parts is the bicentenary of the Stockton and Darlington railway, the 150th was pretty big.

https://www.thenorthernecho.co.uk/news/ ... -revealed/

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https://www.yfanefa.com/record/27024
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Re: How prone are the two Severn Bridges to swaying?

Post by RJDG14 »

KeithW wrote: Mon Aug 01, 2022 16:34
RJDG14 wrote: Mon Aug 01, 2022 14:44 I meant the 19th Century suspension bridge, not the newer looking bridge on the right that was also likely from the 19th Century.

That one is positively modern :)

The sequence goes like this

1) 1830 the suspension bridge.
2) The 1844 Stockton Railway Bridge designed and built by Robert Stephenson
3) The 1881 bridge which had the track lifted but existed until 2008.
Image
4) The 1906 bridge built of steel on the masonry piers of the 1844 bridge
5) The modern bridge built on the site of the the 1881 bridge which was demolished to make way for it.
I think the "one on the right" that I mentioned is probably the 1906 bridge. Edwardian-era architecture feels similar to that of the late 19th Century, so I was close enough.
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Re: How prone are the two Severn Bridges to swaying?

Post by RJDG14 »

I've found some video clips taken via zoom lenses of the original Severn Bridge in 40mph or so winds while open to traffic and it does look in these clips like there is some very slight deck motion, though it's probably not something you're likely to feel. It reminds me a tiny bit maybe of the subtle motion of a modern stabilised car ferry in calm seas.
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Re: How prone are the two Severn Bridges to swaying?

Post by ForestChav »

solocle wrote: Mon Aug 01, 2022 09:53 On the Severn Bridge, it really does feel like there's barely anything between you and the motorway - because, other than a knee high wire barrier, there isn't. Of course, the M48 is hardly a busy motorway these days, so I actually like it - the exposure gives quite a buzz. But it probably wouldn't be so pleasant if it was the M25.
I'd be inclined to agree with this. Though the M48 was down to 1 lane the other week when I was in the area (and went over it a few times) it did feel like a cyclist may be a bit close uncomfortably so to the drivers, and there was only a small fence in the way as well as it being above the cycle/footpath to the outside. It did feel as though a driver making a misjudgement could easily end up on the cycle path and that this may cause injury.

What was slightly interesting, but maybe a touch OT, is the various places you can get "near" the bridge: the new Aust services are somewhat a dive, perhaps even worse than the ones on the A34 just north of Winchester, but most people will use the M4 anyway now - but, of course you can still walk along past the old building to the view point as well as across the bridge where the tolls used to be, which is a decent photo opportunity. And on the other side, you can head through Chepstow and turn down the isthmus between the Severn and Wye estuaries and actually get under the bridge pretty much opposite the Severn from there.
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Re: How prone are the two Severn Bridges to swaying?

Post by ForestChav »

RJDG14 wrote: Thu Aug 11, 2022 20:52 I've found some video clips taken via zoom lenses of the original Severn Bridge in 40mph or so winds while open to traffic and it does look in these clips like there is some very slight deck motion, though it's probably not something you're likely to feel. It reminds me a tiny bit maybe of the subtle motion of a modern stabilised car ferry in calm seas.
I think the issue with high winds (compared to the new bridge) is the sides, there are better windbreaks on the side of the new bridge which would probably dissipate the wind without causing a collapse effect on the bridge which a large inflexible side would do, which means that lorries and higher-sided vehicles aren't susceptible to being moved as much. The old bridge doesn't have this kind of protection and would probably cost more than the benefit of retrofitting it, especially since it's a bypass.

Apparently there was effort to downgrade it between the Chepstow and Aust junctions (the rest would clearly still have to be basically slip roads to the M4) but probably wasn't worth the effort signing it, though they clearly had to do this when renumbering M4 to M48.
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Re: How prone are the two Severn Bridges to swaying?

Post by RJDG14 »

ForestChav wrote: Thu Aug 11, 2022 21:11
RJDG14 wrote: Thu Aug 11, 2022 20:52 I've found some video clips taken via zoom lenses of the original Severn Bridge in 40mph or so winds while open to traffic and it does look in these clips like there is some very slight deck motion, though it's probably not something you're likely to feel. It reminds me a tiny bit maybe of the subtle motion of a modern stabilised car ferry in calm seas.
I think the issue with high winds (compared to the new bridge) is the sides, there are better windbreaks on the side of the new bridge which would probably dissipate the wind without causing a collapse effect on the bridge which a large inflexible side would do, which means that lorries and higher-sided vehicles aren't susceptible to being moved as much. The old bridge doesn't have this kind of protection and would probably cost more than the benefit of retrofitting it, especially since it's a bypass.

Apparently there was effort to downgrade it between the Chepstow and Aust junctions (the rest would clearly still have to be basically slip roads to the M4) but probably wasn't worth the effort signing it, though they clearly had to do this when renumbering M4 to M48.
I wouldn't be surprised if some of the M48 signs are patched M4 signs with references to the road and junction number changed.
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Re: How prone are the two Severn Bridges to swaying?

Post by solocle »

ForestChav wrote: Thu Aug 11, 2022 21:08
solocle wrote: Mon Aug 01, 2022 09:53 On the Severn Bridge, it really does feel like there's barely anything between you and the motorway - because, other than a knee high wire barrier, there isn't. Of course, the M48 is hardly a busy motorway these days, so I actually like it - the exposure gives quite a buzz. But it probably wouldn't be so pleasant if it was the M25.
I'd be inclined to agree with this. Though the M48 was down to 1 lane the other week when I was in the area (and went over it a few times) it did feel like a cyclist may be a bit close uncomfortably so to the drivers, and there was only a small fence in the way as well as it being above the cycle/footpath to the outside. It did feel as though a driver making a misjudgement could easily end up on the cycle path and that this may cause injury.

What was slightly interesting, but maybe a touch OT, is the various places you can get "near" the bridge: the new Aust services are somewhat a dive, perhaps even worse than the ones on the A34 just north of Winchester, but most people will use the M4 anyway now - but, of course you can still walk along past the old building to the view point as well as across the bridge where the tolls used to be, which is a decent photo opportunity. And on the other side, you can head through Chepstow and turn down the isthmus between the Severn and Wye estuaries and actually get under the bridge pretty much opposite the Severn from there.
Here's a clip of the crossing - Youtube

But, speaking of the M25, how about this at Runnymede?
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Re: How prone are the two Severn Bridges to swaying?

Post by ForestChav »

RJDG14 wrote: Thu Aug 11, 2022 21:16
ForestChav wrote: Thu Aug 11, 2022 21:11
RJDG14 wrote: Thu Aug 11, 2022 20:52 I've found some video clips taken via zoom lenses of the original Severn Bridge in 40mph or so winds while open to traffic and it does look in these clips like there is some very slight deck motion, though it's probably not something you're likely to feel. It reminds me a tiny bit maybe of the subtle motion of a modern stabilised car ferry in calm seas.
I think the issue with high winds (compared to the new bridge) is the sides, there are better windbreaks on the side of the new bridge which would probably dissipate the wind without causing a collapse effect on the bridge which a large inflexible side would do, which means that lorries and higher-sided vehicles aren't susceptible to being moved as much. The old bridge doesn't have this kind of protection and would probably cost more than the benefit of retrofitting it, especially since it's a bypass.

Apparently there was effort to downgrade it between the Chepstow and Aust junctions (the rest would clearly still have to be basically slip roads to the M4) but probably wasn't worth the effort signing it, though they clearly had to do this when renumbering M4 to M48.
I wouldn't be surprised if some of the M48 signs are patched M4 signs with references to the road and junction number changed.
tbf probably a lot of them are just stickers with an 8 on a blue background.
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Re: How prone are the two Severn Bridges to swaying?

Post by Bomag »

KeithW wrote: Mon Aug 01, 2022 10:15
RJDG14 wrote: Sun Jul 31, 2022 16:18 The Forth Rail Bridge looks pretty well designed for a railway bridge from the 19th Century. The original Tay Bridge looks pretty flimsy by modern standards with little to no high wind support. The original Tacoma Narrows Bridge looked fairly well designed for its day in terms of its suspension and towers but from the pictures and opening booklet that I can find, the main deck looked very basic with virtually no regard made for airflow underneath.
The result so damaged public faith that the Forth Bridge was massively overdesigned. As part of the final testing Two trains, each consisting of three heavy locomotives and 50 wagons loaded with coal, totalling 1,880 tons in weight, were driven slowly from South Queensferry to the middle of the north cantilever, stopping frequently to measure the deflection of the bridge. This represented more than twice the design load of the bridge: the deflection under load was as expected.
Having led the modelling of the Fourth bridge in the 1990s it is not massively overdesigned as such, it was just properly designed. The design load was two 928 tonne trains which was what it still can potentiality take on the main superstructure, the only thing they got wrong is the wind loading. The original design split the loads between the compression and tension members and only calculated load on the leading edge of tension members. The designs standards in the 1990s to account of issue identified since the 1880's such as forced excitation/ flutter and SHM and loaded all the elements of a lattix truss. It still had a health factor of safety even taking into account tension members ended up in compression.

For the Tay bridge while the high spans are post 1879 the low span trusses were reused - cut and shut -with a new double track deck. I cannot remember where they fabricated the original supports (on site?) but the low trusses where constructed with a bit better QC. In fact the iron elements were generally in a better condition than some of the steel used in the second bridge.
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Re: How prone are the two Severn Bridges to swaying?

Post by Bryn666 »

ForestChav wrote: Thu Aug 11, 2022 21:44
RJDG14 wrote: Thu Aug 11, 2022 21:16
ForestChav wrote: Thu Aug 11, 2022 21:11

I think the issue with high winds (compared to the new bridge) is the sides, there are better windbreaks on the side of the new bridge which would probably dissipate the wind without causing a collapse effect on the bridge which a large inflexible side would do, which means that lorries and higher-sided vehicles aren't susceptible to being moved as much. The old bridge doesn't have this kind of protection and would probably cost more than the benefit of retrofitting it, especially since it's a bypass.

Apparently there was effort to downgrade it between the Chepstow and Aust junctions (the rest would clearly still have to be basically slip roads to the M4) but probably wasn't worth the effort signing it, though they clearly had to do this when renumbering M4 to M48.
I wouldn't be surprised if some of the M48 signs are patched M4 signs with references to the road and junction number changed.
tbf probably a lot of them are just stickers with an 8 on a blue background.
At least two of the M48 RCS are patched signs.
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Re: How prone are the two Severn Bridges to swaying?

Post by WHBM »

ForestChav wrote: Thu Aug 11, 2022 21:08 Though the M48 was down to 1 lane the other week when I was in the area (and went over it a few times) it did feel like a cyclist may be a bit close uncomfortably so to the drivers, and there was only a small fence in the way as well as it being above the cycle/footpath to the outside. It did feel as though a driver making a misjudgement could easily end up on the cycle path and that this may cause injury.
The Severn Bridge has been opened for 60 years now, and must have had scores of collisions in its time, but I have never heard of any breach of the tensioned barrier.
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