Forth Bridge: how would you electrify it?

[deltic08]

The ones with beds...

Now I get it. Bit slow on the uptake. Very subtle.

 

[broadgage]

IMHO, it might be simpler to not electrify the Forth bridge and other especially problematic sections.

"Electric" IETs are fitted with limited diesel power that should be ample to cross the bridge. In fact they could probably coast across, but the limited diesel power would provide insurance against being stranded.
Whilst I am not very keen on IETs for reasons given elsewhere, the fitting of very limited diesel power to the nominally electric units is in my view an excellent idea.
I believe that all future electric trains should have a standby power source, either a small diesel engine or a battery. Mainly for limping to the next station when the wires come down, but also useful for short gaps in a generally electrified route.
Whilst it MIGHT be possible to justify conductor rail in the special case of the Forth bridge, it would require modifications to EVERY electric train that might use the route. This would add weight, cost and complication.
The diesel engines already exist, and limited use of them seems the obvious solution.
Similar arguments would apply along the sea wall at Dawlish and in a few other places.

 

[gsnedders]

It's a long distance to coast, and very problematic for trains calling at Dalmeny and North Queensferry given they'll have almost no speed when starting (and I think it's important for traffic flow that they accelerate away from the stations quickly, and both go straight onto the bridge).

 

[snowball]

Whilst it MIGHT be possible to justify conductor rail in the special case of the Forth bridge, it would require modifications to EVERY electric train that might use the route. This would add weight, cost and complication.

What modifications would it require to every electric train?

Edit: just realised you mean Southern-type third rail. I thought you meant overhead rigid conductor. I totally agree that track-level third rail is not a sensible answer.

 

[broadgage]

What modifications would it require to every electric train?

Pick up shoes, which would probably need to be retractable so as not to foul line side equipment elsewhere on the network. Electrical equipment on board to utilise the different voltage for both traction and auxiliary purposes.
There would also be a new approval process to prove that neither the conductor rail, or the power supply thereto, nor the on board equipment would interfere with the signaling.

 

[snowball]

See my edit to #184, which was probably in a time overlap with #185.

 

[AndrewE]

It shouldn't really be very difficult: as I said ages ago back upthread, let's have a standard special limited-clearance pantograph (low and narrow) which can be fitted as an extra to any rolling stock likely to be used in problem places. There are lots of pinch-points on the network that are getting in the way of electrification such as tunnels, overbridges, the Forth Bridge... As most of these could cope with a speed limit (infinitely better than single track or gauntletting) why not just impliment our UK Special Solution?

 

[K.o.R]

so as not to foul line side equipment elsewhere on the network

But seriously, why is the profile of conductor rail not part of the standard clearance profile anyway? There shouldn't be "stuff" in that part of the track.

 

[broadgage]

But seriously, why is the profile of conductor rail not part of the standard clearance profile anyway? There shouldn't be "stuff" in that part of the track.

We now know that rigid OVERHEAD conductor rail was being suggested, whereas I presumed that Southern type third rail was being considered.
See posts #184 TO ~186.

speaking more generally about Southern type conductor rail, the space used by this is not part of the standard clearance profile, probably because in the past no need was foreseen.
When DC EMUs or locomotives are being hauled over some non-electrified routes, the pick up shoes have to be removed or tied up.

 

[Wst71Pa2]

The bridge is 20/50 differential speeds and 20 wrong direction. TCB Signals at entry, mid and end. Forget coasting

Overhead clearance is an issue, contact wire or bar.
Dropping track/third rail, really? Best thing to do would be park this until the wires reach Perth

 

[najaB]

Best thing to do would be park this until the wires reach Perth

That just kicks the problem into the long grass, doesn't solve it. Contact bar and reduced voltage would solve it.

 

[AndrewE]

That just kicks the problem into the long grass, doesn't solve it. Contact bar and reduced voltage would solve it.

...as long as it can be installed extra low so that the pantograph horns don't collide with that diagonal bracing

 

[deltic08]

...as long as it can be installed extra low so that the pantograph horns don't collide with that diagonal bracing

We are just going round and round on this one. Put it out of its misery please someone.

 

[najaB]

...as long as it can be installed extra low so that the pantograph horns don't collide with that diagonal bracing

That's why the reduced voltage - clearance requirement is based on the square of the voltage (IIRC).

 

[NotATrainspott]

This conversation has happened before, almost verbatim.

I cannot imagine there will be any Forth Bridge-specific solution to this problem. There are plenty of other limited-clearance and/or particularly sensitive parts of the rail network where standard 25kV AC may not be the most cost-effective solution. If there is any intention of creating a new standard for electric rolling stock able to run along these sections I'm certain that the industry would find a universal solution for most, if not all, of these cases to minimise complexity. A non-standard pantograph would be a waste of time, since the number of cases it would solve would be small while requiring relatively major changes to rolling stock design. Third rail isn't a solution for new sections since the only permissible system would be side- or bottom-contact which would be incompatible with the Southern Region/Merseyside network and would foul the loading gauge. By far and away the most sensible and most practical solution is self-powered vehicles. This is the solution being used in South Wales and it requires no novel technologies other than the large batteries which are about to be firehosed into all sectors of the transportation market.

 

[najaB]

By far and away the most sensible and most practical solution is self-powered vehicles.

This is true, with reduced voltage OHLE being the second option. This is proven technology with trains that switch between 25kV and 3kV being common on European networks.

 

[deltic08]

This conversation has happened before, almost verbatim.

I cannot imagine there will be any Forth Bridge-specific solution to this problem. There are plenty of other limited-clearance and/or particularly sensitive parts of the rail network where standard 25kV AC may not be the most cost-effective solution. If there is any intention of creating a new standard for electric rolling stock able to run along these sections I'm certain that the industry would find a universal solution for most, if not all, of these cases to minimise complexity. A non-standard pantograph would be a waste of time, since the number of cases it would solve would be small while requiring relatively major changes to rolling stock design. Third rail isn't a solution for new sections since the only permissible system would be side- or bottom-contact which would be incompatible with the Southern Region/Merseyside network and would foul the loading gauge. By far and away the most sensible and most practical solution is self-powered vehicles. This is the solution being used in South Wales and it requires no novel technologies other than the large batteries which are about to be firehosed into all sectors of the transportation market.

It introduces additional weight and technology that is likely to fail when needed. Keep it simple with just tried and tested 25kv.

 

[gingertom]

It introduces additional weight and technology that is likely to fail when needed. Keep it simple with just tried and tested 25kv.

quite so. If the clearance at the diagonal girders can't be achieved then short earthed sections in the 25kv is the way.

 

[furnessvale]

quite so. If the clearance at the diagonal girders can't be achieved then short earthed sections in the 25kv is the way.

Is it beyond the realms of possibility to modify the girders?

Before anyone tells me the bridge is listed or whatever, surely that horse bolts when you start stringing knitting all over it.

 

[najaB]

Is it beyond the realms of possibility to modify the girders?

Beyond possibility, no. But messing around with the basic structure of a 100+ year-old bridge is not something to be taken lightly. It stands to reason that if those girders weren't necessary, they wouldn't be there.

Before anyone tells me the bridge is listed or whatever, surely that horse bolts when you start stringing knitting all over it.

Yes and no. The listing as a World Heritage Site recognises that it's a working structure and specifically allows for limited modification for operational reasons.

 

[furnessvale]

Beyond possibility, no. But messing around with the basic structure of a 100+ year-old bridge is not something to be taken lightly. It stands to reason that if those girders weren't necessary, they wouldn't be there.

Not necessarily true. Many structures, especially early ones when structural design was in its infancy, have redundancy, either deliberate or obtainable nowadays using modern design analysis.

It could be that a reappraisal of the structure could release certain members or allow for modifications.

It is a fact that we have to thank the likes of Stephenson etc for their overengineering which allows us to run 3000 tonnes trains on 25t axle loads on bridges they built for tiny steam locos and 10t wagons.

 

[gingertom]

has a detailed electrification study ever been done for the bridge?

 

[Wst71Pa2]

We are just going round and round on this one. Put it out of its misery please someone.

I tried

 

[snowball]

has a detailed electrification study ever been done for the bridge?

If there has, nobody in this discussion has read its report, otherwise there wouldn't be such a plethora of guesswork.

 

[edwin_m]

Not necessarily true. Many structures, especially early ones when structural design was in its infancy, have redundancy, either deliberate or obtainable nowadays using modern design analysis.

It could be that a reappraisal of the structure could release certain members or allow for modifications.

It is a fact that we have to thank the likes of Stephenson etc for their overengineering which allows us to run 3000 tonnes trains on 25t axle loads on bridges they built for tiny steam locos and 10t wagons.

The Forth bridge was particularly over-engineered to provide reassurance following the collapse of the Tay Bridge. I imagine it would be possible to remove the diagonal girders one at a time and fix them a bit higher.

 

[kilonewton]

Beyond possibility, no. But messing around with the basic structure of a 100+ year-old bridge is not something to be taken lightly. It stands to reason that if those girders weren't necessary, they wouldn't be there.

Not necessarily true. Many structures, especially early ones when structural design was in its infancy, have redundancy, either deliberate or obtainable nowadays using modern design analysis.

It could be that a reappraisal of the structure could release certain members or allow for modifications.

It is a fact that we have to thank the likes of Stephenson etc for their overengineering which allows us to run 3000 tonnes trains on 25t axle loads on bridges they built for tiny steam locos and 10t wagons.

Very true. The Forth Bridge was designed and built post Tay Bridge Disaster. I’m sure modern day analysis of the bridge would show a factor of safety far higher than modern practice. It may well be that any electrification project will have that analysis done as a value engineering exercise.

 

[najaB]

The Forth bridge was particularly over-engineered to provide reassurance following the collapse of the Tay Bridge. I imagine it would be possible to remove the diagonal girders one at a time and fix them a bit higher.

Over engineered, yes. But that doesn't mean that removing them would be easy (or even possible). It may well have been possible that a different design wouldn't have needed them, but they are part of the current design and the analysis needed to prove that they could be (re)moved would be challenging to say the least - especially given that 'as built' and 'as designed' may have a significant delta.

Edit: And if you think the engineering was conservative following the Tay Bridge disaster, imagine being the engineer who said it was okay to modify the Forth Bridge to then have it fail!

 

[furnessvale]

Edit: And if you think the engineering was conservative following the Tay Bridge disaster, imagine being the engineer who said it was okay to modify the Forth Bridge to then have it fail!

That's what engineers are paid to do. I recall that the Forth Bridge already has a restriction on heavy freight use, so some sort of assessment must have already been made. Further assessment would perhaps demonstrate whether modification of the offending diagonal beams would be possible.

I also recall that Brunel's Saltash bridge has needed strengthening for modern traffic needs so, again it demonstrates that such assessments have been made as loads increase.

 

[deltic08]

Over engineered, yes. But that doesn't mean that removing them would be easy (or even possible). It may well have been possible that a different design wouldn't have needed them, but they are part of the current design and the analysis needed to prove that they could be (re)moved would be challenging to say the least - especially given that 'as built' and 'as designed' may have a significant delta.

Edit: And if you think the engineering was conservative following the Tay Bridge disaster, imagine being the engineer who said it was okay to modify the Forth Bridge to then have it fail!

Over engineered, yes. But that doesn't mean that removing them would be easy (or even possible). It may well have been possible that a different design wouldn't have needed them, but they are part of the current design and the analysis needed to prove that they could be (re)moved would be challenging to say the least - especially given that 'as built' and 'as designed' may have a significant delta.

Edit: And if you think the engineering was conservative following the Tay Bridge disaster, imagine being the engineer who said it was okay to modify the Forth Bridge to then have it fail!

The answer is to make a completely new pair to fit above the first pair and then remove the original pair. Modify this pair to fit above the second pair then remove the lower second original pair to fit above the third pair and so on until the whole bridge is done. This way the bridge is not put at risk but will take a long time to modify.

 

[najaB]

That's what engineers are paid to do. I recall that the Forth Bridge already has a restriction on heavy freight use, so some sort of assessment must have already been made. Further assessment would perhaps demonstrate whether modification of the offending diagonal beams would be possible.

Possible? Yes. Easy? No.