Bridges

We have a smaller scale situation at the Nag's field, we have a watercourse which is dry most of the year, but is 2-3 feet below the level of the access to the gate, and we wanted to keep pikies (gypsies) and their like out, so we had a timber lay-across to start with, but with the advent of big 1/3 ton hay bales, the tractor and trailer demolished those, so we had a couple of steel box section ramps built.

We used box as it is pretty available and can be sealed to keep water and rust out. They also had to be 'light' enough for me to mangandle them into the van and back to the farm afterwards.

Even though we used 100 X 100 X 5mm box, these still deflected a fair bit with the weight of the trailer on them.

In your case, you'd need to go for something like 4 pces 250mm H X 150mm W I-beam in a welded up frame with cross-bracing etc. That is going to be a heavy old lump to move, so best to get it right!

Peter

-- Peter A Forbes Prepair Ltd, Luton, UK snipped-for-privacy@easynet.co.uk

Your I beams are going to have to be 12 x 9 inches and about half inch thick ...to avoid deflection over that span .

i would but them all up against each other .you need about 15 of them....upwards of over =A31000 worth of steel.....weld them or bolt them all together .. have them all laying i foot deeper than the road ...and then have twelve inches of reinforced concrete on top of that.

as for the concrete pads ...depends how how solid the ground is ...if its all loose soil you need to go way deeper...pads laid on top of piles if need be.

all the best..mark

I think there is a standard angle for the bottom of your sloping sides that define where your concrete bedding blocks would go as a rule of thumb as to how far from the edge of the bank you need to be. I have 30degrees in my head but that might just be b***ks there's a lot of that in my head!

Steve

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

lorries can

watery bit.

they're under

You want a small Bailey bridge my lad !

They do turn up occassionally at places like Witham Speciality vehicles

AWEM

Because of safety concerns you need it to be professionally designed.

Something like this might be more flexible. Er .. not the bridge itself, but erecting it:

Albeit, it is a *tad* out of a model-engineers reach.

Nick

How about a medium grider bridge?

Great fun to put together for those of us who loved Meccano

Charles

I saw on TV last week that they are replacing every single part of the Golden Gate Bridge in San Francisco in a refurbishment program. No doubt if you made them a good offer, the old parts would still have some life in them....

David

In message , Nick Mueller writes

Apologies in advance for this piece of deliberate thread drift but it looks as if the German troops in Afghanistan are a damn sight better equipped than the Brits ;-(

Well it is stretching a bit. :-)

I don't know your laws, but here, for a bridge that big, it requires at least approved static calculations and a certified shop (welds) to do it. I could calculate it, but I don't know the required security-factors. And 20 tons isn't really just a bit with 7m span.

Laying just I-beams isn't very cost effective. A structure (truss) will be much stiffer and cost less, but will be more work to build and calculate (joints).

Nick

On or around 2 Feb 2007 09:24:50 -0800, "mark" enlightened us thusly:

12" of concrete is a hell of a road bed. It's mostly for vehicles 2T or less - the extra capacity up to 20T is for occasional use, not every day. It needs to be able to support 20T but not stand up to 50 lorries per day. Most of the deliveries are less than that anyway.

don't know what the ground's like until I start digging, really. I had thought about reinforcing them though.

YEAH ...in that case you could probably get away with 6 inches of concrete on top of the girders ...no problem...with a few bars welded up the sides acting to keep the concrete slab in place with 1.5 inch diametre pipes welded up on top of them ... as a dual purpose safety rail .

all the best.mark

How about dropping some big pipes into the river, to allow thw water through, then filling over with hardcore, followed by a layer of concrete.

I must admit I tend to agree with the poster who says you need to get it done professionally, if someone gets hurt due to your bridge failing, then you will be in for one hell of a big compensation bill- and no insurance company will touch an amateur built bridge.

On or around Sun, 4 Feb 2007 00:31:25 -0000, "SimonJ" enlightened us thusly:

hmmm. mebbe so. 's hardly rocket science though - there must be a table somewhere of what an RSJ of a given dimension will support over a given span, add up the weight of the deck and the weight of the maximum load...

I did rather fancy fabrictaing bailey-style girders on-site, but that might work out more difficult in the long run.

I'll probably get on to the local steel suppliers, and see what they say. Provided the material used is well within it's safe loading, I can't see a problem. I'd probably be worth getting a structural engineer to insepct the plans and/or the finished article.

As for the "pipe" approach - could be done. among other things you can get pre-formed rectangular pre-stressed concrete bridge sections, which you just drop in (I presume onto a prepared, flat concrete base) and build the road over the top. I daresay it's pricey though.

On or around Fri, 02 Feb 2007 22:53:25 +0000, Charles Ping enlightened us thusly:

heh.

just put "bridge" into the ebay search engine, 4877 hits.

If you really want to go with I-beams, you should consider a honeycomb-construction. It is a normal I-beam that is cut with a zigzag-pattern, pulled apart, shifted and then welded together again. It is called "Peiner Schnittführung" (Peiner cut / Peiner cutting-pattern ?). Here's a picture (German text):

Ah! You call that "Castellated Universal Beam"

Nick

There is a program called "beamboy" that was written by Richard Getze. It's available for free. That does a nice job of calculating stresses and deflections for beams with combinations of loads and supports. I used it to size the RSJ that holds up the workshop roof. I had to type in an assortment of UK RSJ sizes and specifications in the config file, but that's a simple job. Google should find it (and RSJ specs) for you.

British Steel/Corus/Tata/why-the-hell-can't-we-invest-in-British-industry make monster economy sized zinc dipped corrugated iron for making concrete floors out of. I used the lightest grade for making some over-engineered pit covers:-

look for composite floor decking.

Mark Rand RTFM

again. It is

No, it IS called "Castellated Universal Beam", it's just that you call it "Peiner Schnittführung" for some odd reason

AWEM

On or around Sun, 04 Feb 2007 14:58:23 +0000, Mark Rand enlightened us thusly:

sounds fun, I'll have a look. what was that game... oh yes, pontifex. not a bridge design thing per se, but fun.

I've fired off a couple of speculative emails, one to a lot supplying ex-MOD bridges (Bailey and similar) and one to the local large steel stockists asking what sort of beams they'd recommend.

will see what if anything comes of it.