Ping Austin Shackles

On or around Mon, 5 Feb 2007 19:25:05 -0000, "Andrew Mawson" enlightened us thusly:

coo. I'll have a look, ta.

On or around Tue, 06 Feb 2007 20:32:32 +0000, Austin Shackles enlightened us thusly:

hmmm. the Class 16 bridge kit is 10K plus vat. MGBs are "substantially more expensive", so I rather think not.

I've asked for a quote from someone else whose bridges I very likely won't be able to justify:

Coo, I see I could've got an online estimate for the quickbridge. Nemmind, I've sent 'em an email.

ah. need to be registered, and that's not working. heyho.

"Austin Shackles" wrote in message news: snipped-for-privacy@4ax.com...

I have a friend who works for Suffolk County council bridge dept (engineer) I could email him and ask what you need

Andrew

On or around Thu, 8 Feb 2007 00:52:19 -0000, "Andrew Bishop" enlightened us thusly:

quickbridges, nice as they are, are definitely out - 20K plus for ex-hire ones or getting on for 50K new.

My plan was to have 4 suitable sized I beams, (or maybe 6) in 2 groups so they line up with the expected vehicle track, then have strong decking above each set of beams and a lesser bit of decking in the middle where the heavy stuff can't get a wheel on it, thereby saving weight. Probably use steel treadplate for the decking, or maybe plain steel plate with glue-and-chippings surface.

The heaviest thing that normally would use it is an 18T wagon (4-wheeler), which has an axle loading of 10T on the "heavy" end. So the whole bridge needs a minimum SWL of 10T in the middle of a 9M span.

If it doesn't make life too difficult or expensive, it could be upgraded to take a 24T (6-wheeler) wagon, which typically have a pair of axles at about

9T each, something like a metre apart, so more or less a 20T load in the middle.

what surprises me is how difficult it is to find this information. I'd have thought that structural steel beams would be supplied based on expected load/span and I'd have expected a standard table of figures for such beams, but it seems not, or not that I can find.

I can find various more or less complicated programs which allow me (or would, if ICBA to find out how) to work out stresses in complicated structures, but this is (or should be) a dead-simple standard answer.

On or around Thu, 8 Feb 2007 00:52:19 -0000, "Andrew Bishop" enlightened us thusly:

twould be very helpful, if you could. even information about where to look for the information would be good.

I know that design of structures in general is complicated, but that's why I was going for a simple and, doubtless, less efficient design.

Ask Evan in the home-shop-machinist website about load span etc ...there's practically nothing he does not know .

I would have thought the ones I suggested ...9x12 half inch thick would be well capable ..

yep you are right ...since the wheels don't touch the middle of the bridge ...there isn't any need for them there .

i used to work down the mines ...we used this stuff all the time for roadway junctions ...big stuff like that wouldn't bend it usually pile drives the stanchions into the floor ..floor coming up to meet the roof at the same time.

that was with 100's or maybe 1000's of tons on them not 20 tons.

junctions 20 feet high and 25x 25 feet wide could end up 5 feet high in a matter of weeks....and have minimum of bend in the girders. they would either fail like that or go over (snapping the tie bars) like a stack of cards...that would happen instantly ...you don't want to be around when that happens :0

so I speak from experience.

very important to put bolted tie bars between them though.

ever seen the film Wages of Fear ...that'll give you some ideas on bridge building . two versions available ...the original French version B&W ...and the English remake colour.

logs are used in that film ...lol

All the best.mark

On or around 9 Feb 2007 18:00:53 -0800, "mark" enlightened us thusly:

yeah, great film that. I've seen the original one.

On or around 9 Feb 2007 18:00:53 -0800, "mark" enlightened us thusly:

I daresay they would. The deck is going to have to be attached to the beams anyway, but good point about ties, I found something somewhere else about beams failing due to torsion at a much lower stress than in pure bending, so they have to be stopped from twisting. Although a 9x12 beam ain't gonna twist much - especially if it's got a fattish steel plate bolted to the top web.

Just pop in a few of them, according to my (1932) Dunlop and Ranken catalogue. a 12*8 rsj, of 19 in^2 csa is good for 18.06 t at 22 feet span as a simply supported beam with uniformly distributed load. At

28 ft, 15.5t, but the typeface changes from black to red, indicating "notable deflection at the center of the joist" and breach of the "span not to be greater than 24*joist depth" rule-of-thumb. That's at 8 ton/in^2, 25% of breaking stress. Divide by two for concentrated load at center or distributed vehicle live load.

I saw just what you need, last night. The Railway was playing silly buggers by parking a maintenance train across our level crossing. Flat bed trucks, a good 30 ft between bogies, and marked 40t distributed. A couple of their frames, side-by-side would eat the job. Where do they recycle old rolling stock, these days? Memories of Vic Berry's scrapyard at Leicester, 1970s. :)

Regards,

David P.

On or around Sun, 11 Feb 2007 16:37:16 +0000, David Powell enlightened us thusly:

see, that's the sort of useful stuff that isn't in anyone's lists. I suppose they're all paranoid about being sued.

wonder what "notable deflection" is... I assume "divide by 2" is divide the load by 2.

span is going to be close to 30ft. If for example I used 3 beams each side it should be well strong enough. Considering a static load of 10T in the middle (rear axle of an 18T wagon) say, then each beam is supporting less than 2T, plus of course a proportion of the weight of the deck. If I up the load to 20T, that still works out at a under 4T per beam, which should still be well safe. have to contemplate how heavy the deck will be, but I doubt it'll be more'n about a couple of tons total.

Try 17cwt 3qt per beam at 30 foot length :-) so about 5 tons for the 6 beams.

This isn't at all outrageous and you could swing them into position using an A frame made from a two, sistered, pairs of 2"x6"x20' wood stood on plates in the middle of the stream, guyed to the banks. Two people could move this into position without strain. When luffing the A frame it is very important to have one person controlling the ropes at each end and keeping them in tension at all times. It is also important to realise that you can't push on a rope DAMHIKT!

Obviously an Iron Fairy would be quicker, but could cost more.

Mark Rand RTFM

On or around Mon, 12 Feb 2007 09:46:48 +0000, Mark Rand enlightened us thusly:

I was talking about the weight of the deck, actually. I tend to assume the people making tables of what a beam of given dimensions will carry at a given span would have taken into account the weight of the beam itself. However, the weight of the deck is a (distributed) load in addition to the load the bridge is expected to carry.

probably, but I reckon that if they're brought in on a wagon with a decent-sized Hiab, it should be possible to get 'em off-loaded more or less into place.

Oh yes, very important, that.

On or around Mon, 12 Feb 2007 19:00:18 +0000, David Powell enlightened us thusly:

arrived, TYVM.

As you say, calculations needed. I also need to find out what beams I can readily get, and make a guesstimate as to the weight of decking. load in terms of bridge beams is going to be a combination of distributed load from the deck and dynamic load from the vehicle.

handily, from the looks of it, the figures in red are also in a different typeface.