Nuts

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.

Much as I hate to disagree with Hopper, I have a book entitled "Machine Construction & Drawing" with examination papers going back to 1888, 1889 & 1890 clearly showing the thin nut under the standard nut.

Brian

The correct way to position lock nuts, according to MacGibbons Tech. Drawing for Marine Engineers published in the 1970s (in UK). And woe betide any candidate for his chief engineer's ticket who drew them in the reverse order. I know that forgetting to draw the split pin hole was grounds for a solid F. But nobody was ever known to draw the thick nut on top of the thin one. Unheard of at that time. This was an exam very strictly administered by the Department of Transport etc in the UK and former colonies for engineers responsible for the safety of ship worth millions and the lives of all aboard.

Edited By Hopper on 04/12/2019 09:20:15

Edited By Hopper on 04/12/2019 09:21:56

Edited By Hopper on 04/12/2019 09:22:47

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Exactly so

MichaelG.

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

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

Ian

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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

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

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

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

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

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

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

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.

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

Oooch, any idea what it cost to put right?

Steve

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

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

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

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