North Yorkshire Moors Railway General Discussion

We had a similar thing last year, an email suggesting we had been "selected" for a small business award for South Yorkshire.

Got as far as speaking to them on the phone, realised it was a pay and get some recognition type event, as opposed to actually being based on merit- wasn't cheap either!

 

Although in fairness I was stewarding a DCE, where when we arrived at Basingstoke NR suddenly said a bridge just East of Wool was not able to stand the weight No 9 crossing it. A fine time to decide, especially as the same loco had gone over twice either the week before or the previous week (forget which). Anyway after many phone calls and about a 30 minute delay a 5 or 10 mph pass was agreed, and stayed in place for the rest of the DCE programme that year.

 

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I'm not a bridge engineer but can understand why RA9 locos were/are permitted on what was an RA5 line. It is more than simple weight; dynamics have a large effect, especially hammer blow, and that goes up by the square. Thus, an A4 at 30 mph (the old line speed) as compared with the present 10mph would exert a load of 900/100 =9 times more. There's more to it than this simple calc but it illustrates the point.

 

I'm not a mechanical engineer, but I am an engineer with some training in mechanical engineering; so, with that background, let me offer a few thoughts.

Stone bridges are a generally a whole different kettle of fish from metal bridges, because when they fail, it's usually for very different causes. Not always; both kinds can fail when the footings of the supports are washed away by the actions of flowing water (like the recent Garmouth Viaduct failure on the River Spey in Moray). A 'failing' bridge that's failing for this reason, it generally just incrementally gets closer and closer to the point of collapse. The collapse can be triggered just by the weight of the bridge itself (the so-called 'dead load' - as happened with the Spey bridge); or, a passing load on the bridge may push it past the point of collapse. Note that these failures a not a failure of the body (the usual jargon among mechanical engineers for that is 'structure') of the bridge itself, but a failure of the footings holding the bridge up.

Both kinds of bridges can also collapse as a result of impact damage (the most famous recent example being the Baltimore harbour bridge), but those obviously aren't really 'failing' until the collision - and those failures generally happen shortly after the collision.

As to failures of stone and metal bridges for other reasons, they are usually related to a failure in the bridge structure itself - and that's usually related to the properties of the material. Stone is strong in compression, but not in tension - so stone bridges are usually arched bridges, where the material is loaded in compression. Unless the stone decays (which it might - e.g. limestone, from acid rain), those should be pretty resilient (and have been - 9 of the 10 oldest bridges in the world are stone arched bridges) .

Metal bridges often include elements loaded in both tension and compression. (The common truss has both kinds.) Those usually fail by a tear in an element loaded in tension. The tear may result from corrosion, fatigue (the growth of cracks in metal from fatigue would need a lecture to even begin to scratch, alas), etc (possibly aided by overload). The famous interstate bridge collapse in Minneapolis was a combination of all those.

There is no general rule as to how safe a 'failing' bridge is; it all depends on the failure mechanism: e.g. a metal tear can propagate slowly or quickly.

What exactly is the issue with Bridge 42, does anyone know? Given that it's a stone arch, which does not seem to have supporting pillars in the river, the abutments must be moving?

Noel

 

https://northyorkmoors-publicportal...Next/publicportal/planningapplications/820983

Has a document listing the issues with the bridge

Sent from my LGN-NX1 using Tapatalk

 

Be quicker to list what isn't wrong with it.

 

Ah, thanks. The "Defects Table" was not very detailed (e.g. "Missing brickwork - Location - Varies"), but the "Essential Maintenance Work Document" had a great deal of detail, which enabled me to mostly figure out what the issues are.

To give that, one need to know that Bridge 42 is essentially 3 arched bridges, side by side. (This is not obvious from the usual photographs!) The outer ones, one on each side, are about .25m wide (I didn't see an exact number given), formed out of large stone blocks ("masonry", in the Work Document). Between them is an arch composed of 7 layers of brick (a little less than 1m thick), about 18.5m wide.

This latter span has a number of issues - primarily many bricks missing, mostly from the bottom layer (one missing patch, probably the largest, looks to be about 8 bricks by 2), but also some other issues, such as some cracks. There are a few photos from below, in which one can see some of the issues (they have enough resolution to be blown up for a better look).

How far it is from failure I have no idea - one would need to be an expert in brick bridges, and see it closely, to tell, I reckon. I'm quite happy it has been closed for repair, though!

In looking up a specialized term, I ran across this site: Long Span Arches: Design and Limitations (and associated pages such as A Stone Arch Bridge’s Weight-Handling Abilities); it's about arched bridges made out of stone, not brick, but they have a great deal in common.

Noel

 

Has any maintenance been carried out on the bridge in recent years? It sounds like the sort of structure you should really have an ongoing maintenance plan for.

 

Maintenance costs money. But not as much as waiting until it is no longer maintenance that is required.

 

I wouldn't go that far; I reckon (as a total amateur at brick arch bridges, admittedly) that after the proposed work, it should be good to go for another century or so - then repeat the process (perhaps ad infinitum). Why do I say that?

As I mentioned, most of the world's oldest bridges are stone arches, and many of them must have gone centuries in their multi-millennia lives with no maintenance at all! Brick arched bridges are slightly less robust, but not because brick is less robust than stone (a well-fired brick is almost as durable as stone, as many centuries-old brick houses and walls can attest). Rather, it's that the stones in stone bridges are larger, and shaped so that they are held interlocked by the force of gravity; they can't fall out. The lower bricks in a brick arched bridge are held in by cement; if that degrades, the bricks on the bottom can just fall out - as some apparently have, here. Once repaired, it will be, quite literally, almost as good as new.

The only potential fly is "The full extent of the defects and the work necessary to correct them will only be truly known once the access scaffold is erected and a throughout touch survey can be undertaken" - so don't put absolute faith in the estimated time for the work.

Noel

 

I think that if its repaired fully with a modern waterproof membrane under the track and proper drainage theres a fair chance it will be better than new.

 

I agree; I said "almost" because one can't be sure if the concrete in the upper layers of bricks is as good as it was originally, without inspecting it - which I don't know of any way to do remotely. (No "touch survey" there; although since they are planning on removing everything above the top layer of bricks, they'll be able to check the inter-brick concrete in that layer, which should give a good clue to the rest of it, up high.) Of course, in the upper layers the concrete will only be loaded in compression, so if it is slightly degraded, that will not be a big deal. (The concrete on the bottom layer which failed, dropping bricks into the river, was obviously loaded partially in tension, on the vertical axis.)

The "Essential Maintenance Work Document" makes reference to a group of NR standard measures for repair of brick arch bridges, designed to deal with the most common defects in these aging structures (near-ubiquitous on NR lines); it would be interesting to read those and see what they have to say about that.

Noel

 

Posted elsewhere:
"I have just resigned my membership too. 35 years of support but no more. ............

If I am hit by a bus between now and a solicitor's appointment on the 16th April the NYMRHT benefits to the tune of around £650,000 pounds.

After I've seen my solicitor the railway gets nil, zero, zilch, nada, nothing.
..........
Enjoy your £3490.00 gala dinner ladies and gentleman. You'll pay the price afterwards."

If that is a true statement, and I've no reason to believe it isn't, then that is one heck of an own goal.

(Edited to get rid of some of the vitriol.)

 

The trouble is that we're told that the NYMR's senior managers are reported to not ready Social Media, this news (if true, of course) will go completely unrecognised by hem. One might hope that their attention might be drawn to the post by concerned bystanders, but is there really any evidence that they even care about, or respond to, criticism? Or if there are even any concerned bystanders with sufficient courage to even bring it to their attention?