Nuts

[Martin ConnellyParticipant @martinconnelly55370]

Ega, the answer is that the whole bridge will move as that is what the bull bar is connected to. This is based on an event when the company I worked for had a large load on a trailer travelling on a motorway that hit a concrete bridge far more substantial than this one. The bridge span moved about 300mm. I have photos somewhere and will see if I can find one showing this movement if you want.

Martin C

[Ian PParticipant @ianp]

Posted by JasonB on 04/12/2019 07:38:58:

Ian, I think you are seeing 6 fixings but the top ones into the concrete have a rectangular "washer" not square like the lower 4

Yes you are right, on closer inspection I can see the large rectangular plate on the top bolt.

Ian

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Martin Connelly on 04/12/2019 10:04:00:

Ega, the answer is that the whole bridge will move as that is what the bull bar is connected to. This is based on an event when the company I worked for had a large load on a trailer travelling on a motorway that hit a concrete bridge far more substantial than this one. The bridge span moved about 300mm. I have photos somewhere and will see if I can find one showing this movement if you want.

Martin C

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That would be very interesting, Martin …Yes please !!

MichaelG.

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PS. … Found this in the news archive

https://www.manchestereveningnews.co.uk/news/greater-manchester-news/light-relief-for-a-bridge-of-sighs-1104392

and some photos on Flickr

https://flickr.com/photos/ants/16760579210/in/photostream/

Edited By Michael Gilligan on 04/12/2019 10:21:42

[not done it yetParticipant @notdoneityet]

Maybe, there is not so much chance of a motorway-speed collision? Span is rather different, visibility is much reduced, etc, etc.

[egaParticipant @ega]

Posted by Hopper on 04/12/2019 09:15:07:

Posted by ega on 04/12/2019 09:07:03:

Does anyone know the actual result of a tall and heavy vehicle hitting the bull bar at speed?

Given the bullbar is made of half-inch steel plate and upwards, and truck bodies are a thin aluminium skin over a flimsy aluminium framework, take a guess.

 

In your hypothesis, no doubt the result would be like the "top off the double-decker bus" mentioned above. Martin Connelly's post is more like what I had in mind and I look forward to seeing his photo.

That said, Michael Gilligan's link suggests that multiple strikes don't necessarily disable the bridge.

Edited By ega on 04/12/2019 11:32:10

[Martin KyteParticipant @martinkyte99762]

Couple of observations for fun.

Motorway bridge decks are usually on bearings with expansion joints so anything hitting the deck will shift it to some extent.

This is a railway bridge and the bull bar is attached to the abutments rather than the span. Motorway bridges dont really care too much about deck alignment but rail bridges do care about rail alignment. Drive over the QE2 bridge at Dartford and you encounter a succession of joints in the carrageway wich allow it to move sideways in sections. Trying that with a railway line would cause a few issues.

regards Martin

[Martin ConnellyParticipant @martinconnelly55370]

Moved bridge span. The flimsy bits were ripped off and the major part of the load and the vehicle passed under the bridge before stopping.

Martin C

Edited By Martin Connelly on 04/12/2019 13:16:50

[vintage engineerParticipant @vintageengineer]

I was taught that 1 1/2 times diameter was the maximum thread needed any longer thread wouldn't be any stronger.

[Martin ConnellyParticipant @martinconnelly55370]

If there is a likelihood of the stud not being normal to the face of the metal being bolted over it then the nut may have a skewed load on it. This may require spherical washer and seat set underneath the nut to even the loads on the thread or alternatively a longer nut which is likely to be a cheaper option.

Martin C

[Brian Sweeting 2Participant @briansweeting2]

Seems a good way of some useful thread length being preserved for the bullbar that has be removed or replaced after any impact damage in the future.

[Martin KyteParticipant @martinkyte99762]

Posted by Hopper on 04/12/2019 08:24:33:

OMG but the bridge men have put the thin locknuts on second, following the practice of engineers and fitters throughout the 19th and 20th centuries on applications such as big-end bolts on large marine diesels and before that steam engines, instead of adhering to the 21st Century ISO standard ( section 5 of ISO 898-2: 2012 Mechanical Properties of Fasteners made of Carbon Steel) of putting the thin nut on first then the thick one. The science of which is outlined here **LINK**

Science deniers, that's what them bridge men are. Next thing they'll be telling us climate change is a hoax to institute a one-world government. Somebody alert the authorities at once, before the bridge collapses and kills Santa Claus.

,

Edited By Hopper on 04/12/2019 08:28:10

Extracted from the link you gave. Seems to be the case which would make the bridge assembly correct so maybe the bridge engineers are not so daft after all.

If there is a significant amount of fastener extension that would be developed i.e. when a long bolt is used, then using the thin nut on the bottom can be inappropriate. In such circumstances the bolt extension could be such that the thin nut would sustain thread stripping due to the extension exceeding the thread clearance available in the thin nut. Hence the warning that placing the thin nut next to joint is not appropriate in all circumstances.

regards Martin

[S.D.L.Participant @s-d-l]

Posted by Martin Connelly on 04/12/2019 12:58:30:

Moved bridge span. The flimsy bits were ripped off and the major part of the load and the vehicle passed under the bridge before stopping.

Martin C

Edited By Martin Connelly on 04/12/2019 13:16:50

Oooch, any idea what it cost to put right?

Steve

[Martin ConnellyParticipant @martinconnelly55370]

Steve, no idea but I hope there was insurance and happy to not get involved. This was not in the UK and probably not UK drivers. The item was being transported from ship to site and weighed over 35 tonnes plus the vehicle which is why it didn't stop when the collision occurred.

Martin C

[David NobleParticipant @davidnoble71990]

Posted by Hopper on 04/12/2019 08:24:33:

OMG but the bridge men have put the thin locknuts on second, following the practice of engineers and fitters throughout the 19th and 20th centuries on applications such as big-end bolts on large marine diesels and before that steam engines, instead of adhering to the 21st Century ISO standard ( section 5 of ISO 898-2: 2012 Mechanical Properties of Fasteners made of Carbon Steel) of putting the thin nut on first then the thick one. The science of which is outlined here **LINK**

I'm certainly not able to refute the argument in the link here but in the two videos which show the difference between the thin nut on top and underneath, I feel the nuts in each video were tightened differently.

I'm clutching at straws as thin nut to the bottom is so counter intuitive for me!

David

[Martin KyteParticipant @martinkyte99762]

The way I look at it is this. The thin is wedged between the substrate and the big nut and any rotation will tighten the grip between it and the substrate or it and the big nut. It is effectively wedged between the two.

If it's on the top any rotation in the undo direction will loosen it.

regards Martin

[John MCParticipant @johnmc39344]

Bridge strike!

This was a test carried out in 1996 at the Whitehouse road bridges, Swindon. These bridges, a group of 4 I think were at one time the most hit bridges in the country.

I wonder who volunteered to drive the bus?

John

[Roderick JenkinsParticipant @roderickjenkins93242]

Posted by Hopper on 04/12/2019 08:24:33:

OMG but the bridge men have put the thin locknuts on second, following the practice of engineers and fitters throughout the 19th and 20th centuries on applications such as big-end bolts on large marine diesels and before that steam engines, instead of adhering to the 21st Century ISO standard ( section 5 of ISO 898-2: 2012 Mechanical Properties of Fasteners made of Carbon Steel) of putting the thin nut on first then the thick one. The science of which is outlined here **LINK**

Science deniers, that's what them bridge men are. Next thing they'll be telling us climate change is a hoax to institute a one-world government. Somebody alert the authorities at once, before the bridge collapses and kills Santa Claus.

I think the whole thing has been put up by the manufacturers of thin spanners

Rod

Edited By Roderick Jenkins on 04/12/2019 17:01:31

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Martin Connelly on 04/12/2019 12:58:30:

Moved bridge span. The flimsy bits were ripped off and the major part of the load and the vehicle passed under the bridge before stopping.

Martin C

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Thanks for the very impressive photos, Martin

MichaelG.

[Neil WyattModerator @neilwyatt]

For a long time there used to be a bridge over a motorway that had a large I-beam, perhaps 18" deep. There was a big dent in it where something rectangular and about 18" wide with enormous force. Clearly it had been decided that this didn't compromise the bridge as it was there for years.

Also there was abridge in Canada hit by lorries about 100 times before they lifted it up.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by vintage engineer on 04/12/2019 13:03:12:

I was taught that 1 1/2 times diameter was the maximum thread needed any longer thread wouldn't be any stronger.

.

That’s a well-kown, and very convenient, rule-of-thumb … but I fail to see how it can be universally valid.

Thread-form and pitch, materials, and tolerances are all contributing variables.

MichaelG.

[old martParticipant @oldmart]

It looks to me that they are studs passing through the entire width of the bridge. Forces are distributed through the brickwork which will be at least 10 feet thick for a single track. The other bridge was displaced off its bearings.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by old mart on 04/12/2019 20:49:38:

It looks to me that they are studs passing through the entire width of the bridge. Forces are distributed through the brickwork which will be at least 10 feet thick for a single track. …

.

It’s worth looking at the Flickr photos that I found

MichaelG.

[John OlsenParticipant @johnolsen79199]

Further to Neils comment…the 11foot8 bridge is actually in Durham North Carolina at the corner of Gregson and Peabody Streets. The bridge was recently raised 8 inches, so it is now 12 foot 4. This has not prevented someone from hitting it already. Last I saw the total number of collisions was up to 151 See http://www.11foot8.com

There is also a low bridge under a railway line in Needles California which is 8 foot 6 inches, we were in a campervan at the time that would not have made it, but were observant enough to see the signs. (N K St, Needles, California.)

regards

John

[old martParticipant @oldmart]

A bit off the original topic, but try looking at street view of Old Basing, Hampshire, UK, 51-16-22N, 1-02-39W. I ducked when riding a motorcycle under this twin track railway bridge, it is marked 7 foot 9 inches.

[old martParticipant @oldmart]

If I am right about the studs passing from one side of the bridge to the other, it would also explain the nut length and sequence. The nuts would have to be extremely tight, and would cause a large amount of tension stretching of the studs. This could be measured in inches rather than fractions of an inch. A long nut of three diameters or more would be safer to tension than the standard length of nut, and the short nut is probably just there to use up the remaining length of thread, and not as a serious lock nut. It also looks the part to casual onlookers.

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