Tay Bridge's condition

[bella]

I note that locos 60163 and 60009 cannot now cross the Tay Bridge. The A1 Steam Loco Trust's reason for 60163 not crossing it this week (14th) refers to the bridge "in its present condition".

Rightly or wrongly this suggests that the structure which has allowed Pacifics to cross it since time immemorial is no longer as strong as it once was?? Any thoughts?

 

[Silverdale]

It may not be a question of the strength of the structure. It could be that it's a question of gauging (clearances) whereby modifications to the structure itself or updated requirements mean that the currently required structural clearances aren't available.

 

[Dr Hoo]

I suppose that it is a few years ago now but there was a major programme of repair and strengthening from 2000-2006 at a cost of £38 million. On an essentially ‘eternal’ structure such work would normally be expected to be effective for many years.

There has long been a restriction on ‘double headed’ locomotives with the concentrated mass being disproportionately fatiguing. Were the proposed steam locomotive movements associated with ‘back-up’ diesels or something?

 

[Ploughman]

Is this a case of the structures being maintained to the requirements of the regular traffic on the bridge, with no allowance for the out of the ordinary?
What is the axle load on an HST as against an A4?

Or is it due to corrosion?

 

[GRALISTAIR]

There has long been a restriction on ‘double headed’ locomotives with the concentrated mass being disproportionately fatiguing. Were the proposed steam locomotive movements associated with ‘back-up’ diesels or something?

Electrification while putting permanent load on the bridge would help the train to be lighter- electric must be lighter than diesel or steam surely?

 

[bella]

The UK Steam website now says it is due to weight restriction. That appears not to say a lot for the scope of the 2000-6 work?

Have no knowledge of any double heading or diesel being on train. If it was it would be likely to be at rear or following behind rather than on train.

 

[InOban]

The central section - the High Girders - received extensive renovations last year, won awards. I've often wondered whether OHLE clearance will be more of a problem here than at the Forth. How much do these engines weigh?
I'm sure the foundations aren't nearly as deep as they should be.

 

[LAX54]

The UK Steam website now says it is due to weight restriction. That appears not to say a lot for the scope of the 2000-6 work?

Have no knowledge of any double heading or diesel being on train. If it was it would be likely to be at rear or following behind rather than on train.

How heavy is a Steam Loco compared to a Diesel Loco ?

 

[edwin_m]

Something to do with "hammer blow"? (where the off-balance rotating masses of a steam loco exert higher forces on the track)

 

[Silverdale]

The UK Steam website now says it is due to weight restriction. That appears not to say a lot for the scope of the 2000-6 work?

If it is an axle load limit, presumably the decisions about the scope of the 2000-6 work were based on the axle loads of the intended passenger and freight services. If it would have cost more to clear the structure for the axle loading of e.g. Tornado, where would that extra money be found?

 

[Spartacus]

How heavy is a Steam Loco compared to a Diesel Loco ?

If you compare with the heaviest diesels there's not a great amount of difference, the issue is the axle weight translating into route availability, for instance a Peak, which is heavier than a 67 has a better Route Availability due to having that weight spread over more axles. Steam locos are further handicapped by tending to have their weight less evenly distributed than diesel locos, with proportionally more over the driving wheels than carrying wheels.

 

[DarloRich]

The UK Steam website now says it is due to weight restriction. That appears not to say a lot for the scope of the 2000-6 work?

do you know what the issues is or are you simply running on platform ender wibble?

 

[LAX54]

So I assume as we don't run steam trains anymore, there was no need to take those into account.

 

[AM9]

So I assume as we don't run steam trains anymore, there was no need to take those into account.

Officially, yes. This may become a feature of an increasingly cost-concious railway. I think that the general public wouldn't see any problem with that.

 

[bella]

I would have thought a speed restriction for a Pacific would have solved it (less hammering) but maybe that's too complicated for those in charge.

 

[DarloRich]

I would have thought a speed restriction for a Pacific would have solved it (less hammering) but maybe that's too complicated for those in charge.

so the answer to my question at #12 is no then. Perhaps trying to work out what the actual problem is is too complicated for "enthusiasts" to grasp.

 

[Jonny]

I would have thought a speed restriction for a Pacific would have solved it (less hammering) but maybe that's too complicated for those in charge.

I also understand that the high girders section is signalled "virtual single track" in that only one direction may be cleared at any one time, with the other line blocked (by signal on/at danger) and empty of trains. This means that a loco with a very low speed limit, taking its time, would be very disruptive.

 

[DarloRich]

It could be that it's a question of gauging (clearances) whereby modifications to the structure itself or updated requirements mean that the currently required structural clearances aren't available.

I also understand that the high girders section is signalled "virtual single track" in that only one direction may be cleared at any one time, with the other both blocked (by signal on/at danger) and empty of trains. This means that a loco with a very low speed limit, taking its time, would be very disruptive.

there is no place for such technical matters. It is all a conspiracy to stop puffer buffer tours! The interesting thing to know is if any other trains are limited on the route. What, for instance, is the impact on engineering trains and equipment? I suspect that if there is an issue it applies to more than steam trains.

 

[Jonny]

there is no place for such technical matters. It is all a conspiracy to stop puffer buffer tours! The interesting thing to know is if any other trains are limited on the route. What, for instance, is the impact on engineering trains and equipment? I suspect that if there is an issue it applies to more than steam trains.

I believe it applies to freight as well - anything freight effectively has to go via Perth. Especially if it is a potentially RA10 (when loaded) wagon.

 

[Journeyman]

Is this a case of the structures being maintained to the requirements of the regular traffic on the bridge, with no allowance for the out of the ordinary?
What is the axle load on an HST as against an A4?

Or is it due to corrosion?

HST power cars are very light at only 70 tonnes, so 17.5 tonnes per axle. An A4 is 104 tons (loco only) over six axles, so 17.4 tonnes. Surprisingly not much in it.

 

[gsnedders]

HST power cars are very light at only 70 tonnes, so 17.5 tonnes per axle. An A4 is 104 tons (loco only) over six axles, so 17.4 tonnes. Surprisingly not much in it.

I would be unsurprised if to some degree the concern is as much about the total weight on the high section as it is about axle loadings.

 

[Ploughman]

HST power cars are very light at only 70 tonnes, so 17.5 tonnes per axle. An A4 is 104 tons (loco only) over six axles, so 17.4 tonnes. Surprisingly not much in it.

I was under the impression that an A4 or similar was approx 23t on axle loading, remembering that not all axles carry the same weight.

 

[Spartacus]

HST power cars are very light at only 70 tonnes, so 17.5 tonnes per axle. An A4 is 104 tons (loco only) over six axles, so 17.4 tonnes. Surprisingly not much in it.

The max axle load of a Tornado is 22.1 tons according to wikipedia, so there's the best part of 5 tons in it, it's quite a bit really.

 

[DelW]

I would have thought a speed restriction for a Pacific would have solved it (less hammering) but maybe that's too complicated for those in charge.

That's easy to say when you're not the one having to sign off a loading as safe. In my professional life (construction not railways) I regularly have to assess structures and approve them for various loadings, and nothing concentrates the mind like having to put your signature on the approval, knowing that potentially lives are at stake if you've got it wrong.

Unless they have been superseded by a Eurocode (which I haven't used as my involvement with railway bridges was a few years ago), railway vehicle loadings are specified in what was British Standard BS5400, now forming Appendix A of BD37/01, itself being part 14 of the Design Manual for Roads and Bridges. The relevant loading for main line railways is RU loading to clause 8.2.1, with dynamic effects as clause 8.2.3. RU loading is explained in Appendix D of BS5400, which shows it as based variously on B-B and C-C locomotives, including double-headed, 4-axle bogie wagons, and exceptional wagons with more (up to 14) axles. There is no reference to steam locos that I have found, so unless there are documents from other sources covering them, it's possible that an engineer making assessments for them has to work outside the current codes. The high un-sprung reciprocating masses of a steam loco's motion may well produce dynamic loads well in excess of those from a diesel or electric loco, and it would be interesting to know how engineers carrying out bridge assessments for heritage lines determine their loadings.

The nominal static axle load in RU loading is 250kN = 25.5 tonnes, but the dynamic factors can increase the resulting forces by up to 2.0 times. The vehicle axle loads for the various types as listed above are between 20 and 25 tonnes per axle.

 

[DarloRich]

That's easy to say when you're not the one having to sign off a loading as safe. In my professional life (construction not railways) I regularly have to assess structures and approve them for various loadings, and nothing concentrates the mind like having to put your signature on the approval, knowing that potentially lives are at stake if you've got it wrong.

that is the point - most of the people complaining will never be in that position and so don't understand either the responsibility or the risk.

 

[d9009alycidon]

The Tay Bridge will never fall down!



Signed
Sir Thomas Bouch

 

[matchmaker]

The Tay Bridge will never fall down!



Signed
Sir Thomas Bouch

You are SO wrong!

Signed
Colonel Yolland

 

[HaggisBotherer]

Electrification while putting permanent load on the bridge would help the train to be lighter- electric must be lighter than diesel or steam surely?

Which is the obvious solution to the thread topic of those well-known electric locomotives 60009 and 60163 not crossing it...

do you know what the issues is or are you simply running on platform ender wibble?

I think you know the answer to that with any post on any thread which includes "That appears..." or "I would have thought...", DR

 

[HaggisBotherer]

The max axle load of a Tornado is 22.1 tons according to wikipedia, so there's the best part of 5 tons in it, it's quite a bit really.

Do you mean a Tornado F3 or GR4, though?

 

[furnessvale]

Has any thought been put to the possibility that modern bridge assessment techniques have realised that the bridge is not (and has never been) as strong as assumed, thus more restrictions have been applied?