Nuts

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

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Thanks for the very impressive photos, Martin

MichaelG.

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.

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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.

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.

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

MichaelG.

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 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

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.

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.

If you are right about the studs passing through the whole structure then I think they would have to be put in position when the bridge was built.

How on earth could a 1" or so hole be so accurately drilled (guided) over that length and end up in line with

the holes in the bracket?

Ian P

I remember looking at this one while sat in traffic that would tend to indicate studs that don't go all the way through though they may be bonded into middle earth.

Same long nuts but no locknut and a smaller diameter fixing at the bottom.

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More later ... I’m off to the Dentist

MichaelG.

The dentist should be knowledgeable on the subject of drilling, maybe discuss (not easy when your mouth is otherwise occupied)

Ian P

Not knowing whether drilling a horizontal hole that long is possible without a large error at the other side, lets now assume the holes are blind. They would have to be at least 2 feet deep in the brickwork, and bonded in using one of the modern glues, or the self mixing glass tubes of epoxy. The studs are a good 40mm diameter, judging from the adjacent brickwork. A bonded in threaded stud will probably break before pulling out. The extra length of stud sticking out is insurance against damage, and allows a long screwed on fitting while driving them home with the hole partially filled with glue.

The dentist was not a lot of help [he's better with canals] ... so I took a few more photos

Here are the four corners:

Observant viewers will note that the upper 'studs' are horizontal at the high end of the bridge, but all the others are perpendicular to the buttresses.

MichaelG.

And here's the 'product shot' of the nuts:

MichaelG.

Oh, I don't know, MichaelG, mine is good at bridgework also
DaveD

It is possible, I suppose, that the deep 'nuts' are in fact spacers , or nuts with the thread bored out. This would allow for a longer section of the bolt to be involved, allowing for greater elasticity, and better fatigue resistance. But I expect that this is just 'how grandad did it' in modern terms, even though grandad never went to college.

Cheers, Tim

Hi, I see, tapered washers on the two bolts into the concrete section, as you wouldn't want a long bolt at an angle with such a slim section, relatively. As far as rebar is concerned, there are drills that will cut through rebar especially water cooled diamond core drills. When I worked in my old job as a maintenance engineer, several machines had the thin nut on top fitted by the manufacturers, one in particular I remember was a vibrating screen, which was about 1.5 M wide by 5M long and it had two vibratory boxes attached to a very heavy cross I beam, each box had four 1-1/4" UNF bolts holding it onto the beam. When we had to transfer the boxes onto a new screen frame, these bolts had to be replaced and tightened up with a slogging spanner and the thin nut went on top, all as per manufactures instructions.

For those who haven't heard of a slogging spanner, it is one that you use with a dirty great big hammer and in the case above, it was a long handled lump hammer.

Good clear photos by the way Michael.

Regards Nick.

Edited By Nicholas Farr on 07/12/2019 12:06:03

Theres been some mention of bolts passing through the width of the bridge. The large "washers" on this bridge are fitted to through bolts to repair and strengthen the structure. The bridge is on the London/Bristol main line. I remember it well, this bridge was on my daily commute and the road closure and traffic lights caused chaos. I felt very smug as it made little or no difference to me as I cruised by the long, long queue of traffic on my bicycle!