Black Bridge, Nuneham: southern abutment failure

[whole diary]

[stuving]

600mm. Blimey. Impressive.

It's what was needed - indeed, exactly how far I estimated the deck to have dropped from its original height, by peering intently at pictures taken along the track. Presumably it will have to go a bit higher to add the bearings on top of the new abutment.

But you'll observe that the lift was not done in one go - none of the jacks has extended by anything like 600 mm. They will have been used as two sets alternately: lift the bridge on one set, raise the second on spacers (which you can see), then lift using those and retract the first ones to add more spacers under them.

[ellendune]

Here's the picture from Twitter:



Well I tried.  Why can I only get that to work 50% of the time?

I was going to add that that is just as I imagined it would be done. 

Now the real work can start on the new abutment. 

Is this the problem I describe at http://www.passenger.chat/27456 ?

Depends if anyone else can see the image which is the one that Red Squirrel posted

[CyclingSid]

Image from https://twitter.com/507stre/status/1655619283479560196
Additional image https://twitter.com/507stre/status/1655988513806901249?cxt=HHwWgoCz2fGxoPstAAAA

[Red Squirrel]

[...]

Depends if anyone else can see the image which is the one that Red Squirrel posted

Can you see it, ellendune?

The uri you posted was: https://twitter.com/507stre/status/1655619283479560196/photo/1

This appears to link to the twitter page, rather than directly to the image. I can see that the img tags wouldn't like that!
The uri I posted was: https://pbs.twimg.com/media/Fvnw9uMX0AIqpPz?format=jpg&name=small

...which is clearly very different. This does resolve, and works within the img tags. I note that it needs the querystring (the ?format=jpg&name=small bit).

I don't claim to be an expert in either twitter or simplemachines; I have posted this in the hope that it helps!

[stuving]

For those that can see that picture ... doesn't the platform the jacks are sitting on - piles, lattice girders and all - look massively over the top for the load they are carrying (which is about 120 tons total)? Even if it's rigidity that counts, rather than strength, that's still true.

[ellendune]

For those that can see that picture ... doesn't the platform the jacks are sitting on - piles, lattice girders and all - look massively over the top for the load they are carrying (which is about 120 tons total)? Even if it's rigidity that counts, rather than strength, that's still true.

Possibly, though the trusses are only supported at the ends so there is quite a long span. The loads may not be evenly distributed among all the jacks that support the deck or if there is some differential settlement in the piles. There will also need to be some allowance for accidental and construction loads on the bridge deck.  Finally they will be using what they had available in the yard at short notice. 

[CyclingSid]

See last two pictures for an idea of how much of the embankment has been removed at this stage
https://www.tmsmaritime.co.uk/emergency-works-2/

[Electric train]

For those that can see that picture ... doesn't the platform the jacks are sitting on - piles, lattice girders and all - look massively over the top for the load they are carrying (which is about 120 tons total)? Even if it's rigidity that counts, rather than strength, that's still true.

Possibly, though the trusses are only supported at the ends so there is quite a long span. The loads may not be evenly distributed among all the jacks that support the deck or if there is some differential settlement in the piles. There will also need to be some allowance for accidental and construction loads on the bridge deck.  Finally they will be using what they had available in the yard at short notice. 

I agree with ellendune observations.  Also when I have been involved in projects where temporary support structures have been put in place the design always looks OTT^▸ (Open Train Times website), it was explained to me by a structural engineer the temporary steel beams used have a lower load rating than structural steel RSJ^▸ (Rolled Steel Joist, which can also be called ) 'I' beams of an equivalent size

See last two pictures for an idea of how much of the embankment has been removed at this stage
https://www.tmsmaritime.co.uk/emergency-works-2/

I guess they need to make space for the piling rigs, and may be they also needed to remove that far back to get to stable embankment

[Bob_Blakey]

I wouldn't have thought the embankment would be cut back further than absolutely necessary - to do otherwise would increase the cost and duration of the repair -  so somebody must surely have concluded there is an awful lot of unstable ground around the south abutment.

[stuving]

I wouldn't have thought the embankment would be cut back further than absolutely necessary - to do otherwise would increase the cost and duration of the repair -  so somebody must surely have concluded there is an awful lot of unstable ground around the south abutment.

Moving earth around has got so quick and easy with modern machinery that I don't suppose it's a big issue any more. You have only to look at any building site, even a couple of houses, to see how much moving earth back and forth goes on and how few people it takes to do it.

So I think it looks like working space they are creating. I'm sure there will be very strict rules and restraints to prevent anyone working underneath that bridge of Damocles. Incidentally, I've seen no sign of anything holding that span in place, to prevent it moving on or off its bearings or the jacks. Surely that's essential in a case like this?

[Mark A]

New Friday video from Network Rail Western.

https://twitter.com/networkrailwest/status/1657030370897055744

I'm no closer to understanding how that bridge's bearings work. We could do with a few close up quality photos of the, um, ends.

Mark

[Electric train]

I wouldn't have thought the embankment would be cut back further than absolutely necessary - to do otherwise would increase the cost and duration of the repair -  so somebody must surely have concluded there is an awful lot of unstable ground around the south abutment.

Moving earth around has got so quick and easy with modern machinery that I don't suppose it's a big issue any more. You have only to look at any building site, even a couple of houses, to see how much moving earth back and forth goes on and how few people it takes to do it.

So I think it looks like working space they are creating. I'm sure there will be very strict rules and restraints to prevent anyone working underneath that bridge of Damocles. Incidentally, I've seen no sign of anything holding that span in place, to prevent it moving on or off its bearings or the jacks. Surely that's essential in a case like this?

As is often the case nowadays the back fill can be blocks made from a styrene based product which does not require compacting.

New Friday video from Network Rail Western.

https://twitter.com/networkrailwest/status/1657030370897055744

I'm no closer to understanding how that bridge's bearings work. We could do with a few close up quality photos of the, um, ends.

Mark

A quick Google provided this definition - Bridge bearings are the devices that transfer the traffic loading and the weight of the bridge from the superstructure to the substructure. Bearings also allow the bridge to expand and contract, as well as allowing for rotation of the beams as they deflect under live loads.
This webpage might help https://theconstructor.org/structures/bridge-bearings-types-details/18062/

[Mark A]

That page is a good resource - I meant to say it's not clear what the provision is at Nuneham.

The pair of bowstring spans look to be in contact at the pier in the centre of the river: perhaps at the landward end of each there are simple sliding bearings to provide for movement and those are prone to seizing - at the time the bridge was reconstructed before 1910, engineers would have been familiar with various types to cope with different types of motion and loadings.

There's also the question of whether the design of the bearings allowed the failing span to start 'Walking' laterally.

The choice of bearing is a bit of a window into the understanding of the designers of the structure - the nature of the movement that at the time they antipated they'd need to cater for. Network Rail will have something in hand on this though.

Mark

[paul7575]

My thoughts are that they’d somehow link the two spans in the middle, and make that a single fixed point, with any sliding being done at both the land abutments? 

That would be logical for ease of access if the sliding surfaces or maybe rollers had to be maintained.

Paul

[ellendune]

From my short time designing bridges I recall the following:

1) You need rotation at both ends though only one end needs to slide.  Both ends should be maintained. 
2) Always overdesign the bearings - they sound expensive, but replacing them is more than 10 times the initial cost and over 100 times the marginal cost of a bigger bearing!

Modern elastomeric bearings may require less maintenance than the traditional roller bearing designs used when the bridge was built, but I don't know if they would be suitable for this type of bridge where the load is transferred at the corners of each deck.