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Bridge that Gap: Great Central Railway News

Discussion in 'Heritage Railways & Centres in the UK' started by Gav106, May 8, 2010.

  1. Flying Phil

    Flying Phil Member

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    Indeed the new bridge abutments are massively engineered with lots of very deep long piles.......I asked at the time it was built and the description was " if the Bomb goes off over Loughborough, the only things left standing will be these abutments!" I suspect that the reason why there is still a gap to the North embankment, is that they want to have the South "Factory Flyover" section in place at the same time to keep the forces in balance...? (Not a structural engineer though :rolleyes:).
     
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  2. pmh_74

    pmh_74 Member

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    Martin - Is it any more surreal than that canal aqueduct over the M6 toll road?

    Phil - I suspect the embankment at the north abutment simply wasn’t in the contract for the bridge works. My guess is it will be bundled in with the embankment at the other end of the project, since it will require the same skills and machinery.
     
    Last edited: May 20, 2020
  3. Bikermike

    Bikermike New Member

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    The Lichfield Canal Aqueduct is a key sight on any trip up to the north/northwest for us, "spot the aqueduct" is part of the journey.

    I'm surprised no one has ever tried to put a dummy boat on it to confuse people.

    I'm not surprised the abutments are large - as you say, normally, it would lean on the embankments each side. Also, NR are presumably not going to take a laid-back view about a bridge falling over on the Midland Line. I wonder if they have considered any risk of them having to take it over at some point - is it designed to take full modern track requirements if needed? Mass concrete isn't that expensive if you pour it all in one project. Putting a tonne in, and finding you need an extra tonne later is way more expensive than pouring three tonnes now.
     
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  4. pmh_74

    pmh_74 Member

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    Is it not more the case that on most bridges, we don't see how big the end abutments really are as part of the structure is usually buried in the embankment? Here, it's exposed so it looks bigger than we're used to.

    Also, I may not have remembered this correctly but I thought the bridge was actually owned by NR (though paid for by GCR/donors) because only NR had the requisite level of insurance cover for the very specific risks of maintaining a structure over a live and (potentially in future) electrified railway. Or something like that. It was reported in either 'Main Line' (GCR in-house magazine) or on the website shortly after completion. So far from taking it over 'at some point', I believe they already have.

    As far as 'modern track requirements' go I'm not sure what you mean, but the GCR has an axle loading which allows pretty much anything to run and I can't see this bridge being specified any differently. It was, after all, designed and built by professional civil engineers who do this stuff for a living, and they will have had to adhere to Network Rail standards. I really can't see any issue with it at all.
     
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  5. Bikermike

    Bikermike New Member

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    yes - you need more Public Lability insurance to play with the railway than you do at an airport.
    Makes sense that they own it, after all if the GCR goes under, they'll have to maintain it. Then from there, like any utility, you specify it to the nth degree when someone else is paying for it to limit your risk later.

    In terms of track standards, I was originally going to say "axle loading", but then that is likely to at least as high for the GCR as it is for the mainline. I was more wondering about the equivalent of building a new-build steam engine with the requisite build paperwork to allow future use on the mainline (but the other way up). They may be to a higher standard anyway, but for "track standard" read [whatever a 66 and a thousand tons of aggregate trundling at 60 needs] to the extent it's higher than an A4 with 8 mkIs on.

    NR's standards would in theory only be to do with making sure nothing fell off it onto the track below in this context, as it's not their railway.
     
  6. huochemi

    huochemi Well-Known Member Friend

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    ISTR that NR wanted (and got) the local council as the counterparty as they did not want to take a view on the creditworthiness of the GCR plc.
     
    Last edited: May 20, 2020
  7. Flying Phil

    Flying Phil Member

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    I think that there is a fairly complex arrangement behind the MML/GCR bridge but all must have been resolved well to get it built. Of course the present GCR have run the line longer that the GC or LNER or BR ran it!
    Still it is great to see that the fundraising for the "Factory Flyover" is proceeding at a good pace with another £50,000 raised since March.
     
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  8. Davo

    Davo Member

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    It seems to me as well the london extension G.C.R. proper used to overlap other railways alot like the new one at loughborough coming south out of sheffield from woodhouse jct and through notts and rugby on similar structured iron work girder bridges or steel bridge deck spans
     
  9. Bikermike

    Bikermike New Member

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    A local authority will always be a better risk than a private company, so I'm not surprised that NR wanted it as counterparty.

    With regards to previous practice, I don't think they ever did "bridge first embankment later". But the GC mainline was the last one, so you'd expect it to have to over other railways.
     
  10. weltrol

    weltrol Member Friend

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    Go and look at Beddgelert. The proposed route of the NWNGR from the Goat tunnel was to have crossed the A498 - the bridge was built - then crossed the Glaslyn valley on an embankment, an underbridge was needed, so the abuttments were built, but nothing else...
     
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  11. pmh_74

    pmh_74 Member

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    I don't understand what point you are trying to make here. A 'Peak' weighs more than a 66, about 133T (45) or 138T (46) in fact, and there is one at GCR and another at GCRN, so at some point they are bound to double-head, and 271T will bear down on that bridge. The bridge is not quite as long as two 'Peaks' so the figure may be a little less overall, but still over 200T if we consider three bogies bearing down on it. The point is that the GCR heritage fleet can throw at this bridge anything equal to whatever you will find on Network Rail. And the design will have allowed for that.
     
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  12. Bikermike

    Bikermike New Member

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    They don't run at speed though do they. And whatever 8 coaches of portly rail enthusiasts weigh, I'd guess a full train of modern ballast hoppers weighs more.
     
  13. Bikermike

    Bikermike New Member

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    I was really only referring to the gc mainline, I don't know the one in question
    Did they build embankments?
     
  14. Flying Phil

    Flying Phil Member

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    I too am not quite sure what point Bikermike is trying to make? The GCR bridge over the Midland Main Line has been designed and built in full compliance with all the relevant NR requirements. Yes it is a massive structure and yes it will take two "Peaks" or double headed Pacifics as per the rest of the GCR. I bet they have even considered stone traffic from Mountsorrel as a Very Very faint chance!
    I'm just pleased that the GCR are making steady progress across the "Gap"....and if we continue to donate, that progress will be faster!
     
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  15. Bikermike

    Bikermike New Member

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    My point is this: dynamic loads have as much to do with speed as much as weight. If the GCR specced it to preserved railway standards then any calculation assumes either 25mph (usual preserved railway) or maybe the 50mph derogation the southern gcr has. If NR are soley concerned about protecting their current line, then they will simply ensure that it is designed so nothing will cause the bridge to fail when used to the above speeds. To say it's built to NR standards is missing the point - NR standards for an overbridge will not determine if it is suitable for a modern railway to run over it.

    No matter what the axle loads the gcr can conjure up, if they only run at 25/50mph, it's a very different calculation to whatever NR spec new lines to (100? 125?) and the additional forces that that entails. Force generally goes to the square of the speed AIUI.

    If everyone takes the short-term view, you get a bridge that won't obstruct the NR railway with a low-speed railway over it..if everyone takes the long-term (or possibly WIBN) view, you get a bridge capable of taking modern traffic at NR speeds.

    It will be massively cheaper to build it to the higher standard now than to upgrade later. The question is the odds of later ever happenning
     
  16. Flying Phil

    Flying Phil Member

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    I think the GCR and NR have taken the long term view - those bridge abutments are solid reinforced concrete blocks with blue brick facings. They are built on integral reinforced concrete piles going down 15m. The bridge deck is designed and built to current NR standards.
    I don't think that the speed of the trains is as significant as the many other factors involved in bridge design. Certainly the "Hammer blow" of steam locomotives reciprocating masses is speed proportional, but modern electric and diesel engines have much lower dynamic loads. After all many Victorian designed and built structures are still in use on the network with "modern traffic at NR speeds". True the blue brick gives it a more traditional look but I suspect the engineering is very nearly to HS2 spec.
    Which brings up another aspect ....who would have paid for a "Higher standard" bridge? NR would never get permission for such an isolated bit of infrastructure on the off chance that HS 5 might come that way. The GCR? why would they pay for something that could destroy their "Raison d' etre".........
    Besides, it is built now....to a very high standard, so worry not Bikermike and look forward to joining a "train load of portly enthusiasts" at some time travelling over the bridge!
     
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  17. Johann Marsbar

    Johann Marsbar Member

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    They are doing an online talk on 31st May about the Reunification project, if you make a donation.
    Details here....http://www.gcrailway.co.uk/unify/
    Limited to 100 participants a time on Zoom (as i found out earlier this week whilst trying to join an online NTA meeting...), so they will run other dates given the 100 limit being exceeded.
     
  18. pmh_74

    pmh_74 Member

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    D123 is regularly used on testing contracts, and testing contracts run at up to 75mph. It's almost certainly been the fastest 'Peak' in the country ever since 45112 was retired from the main line.

    Not that that makes the slightest bit of difference. *IF* some hypothetical future freight flow were to materialise which required the heaviest trains to use this bridge, they're still not going to be any heavier than a pair of Peaks *at the point of acting on the bridge* and they're highly unlikely to trundle through an increasingly residential area at more than 25mph either. But this is such a fanciful *IF* that we may as well forget it. I believe one of the earlier models for funding this project considered extracting both stone and money from Mountsorrel quarry, but the idea was abandoned early on. Which I have to say is a good thing; it may have got the gap filled quicker but it would have required so many upgrades to the existing 'heritage' railway infrastructure that it would have destroyed much of the 'heritage'. It would also have rapidly alienated the GCR's neighbours and core supporters. So I can't see that idea ever coming back, especially once the link has been paid for by enthusiasts.

    What I don't understand is why you think NR would have allowed any sort of 'lower specification' bridge over their railway; they weren't paying for it, so they have no vested interest in keeping costs down and could insist on whatever they liked. And while there are plenty of things to criticise the modern railway for, being slow to spend other people's money isn't one of them.
     
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  19. Bikermike

    Bikermike New Member

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    You've answered your own question. NR specifications apply to keeping NR safe. Otherwise you'd be saying every footbridge over the line has to be built to carry a railway. NR specs will (unless they go the extra mile) be to ensure it won't fall on the railway below under planned usage. So on the one hand ypu are saying it is WIBN to build it to carry modern freight, and then elsewhere you are saying you don't understand the question becuase it's built to NR standards - which is it?
     
  20. Flying Phil

    Flying Phil Member

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    I think that you need to read the post from pmh more carefully Bikermike.....he said that it was for funding that the freight flow model was considered. The bridge now built is more than capable of handling the trains likely to be carried....or even unlikely to be carried, at any speed that the railway is legally allowed to use. NR are also more than happy with the bridge that they have specified.
     

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