6m 'bridge' using decking materials?

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The Natural Philosopher wrote:

That would *definitely* require a well engineered structure (or some really big tree trunks).

Exactly! That's what I've been saying. It really isn't that big a span, and using 3off 9"x3"s would give a very sturdy bridge with next to no deflection with a couple of people standing on it.
--
Grunff


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Grunff wrote:

I am sure the OP said 30m. ooh. 19'. Mm. I read that s 19 meters, or about 60'.
OOPS :-(
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wrote:

SC3 is now GS = C16
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On Mon, 01 Dec 2003 18:29:57 +0000, David Hemmings

Ah, right, that's cleared that up then. ???????? :-(
If I go to my local builders merchant and ask for three, six meter long, 75mm by 225mm tannelised joists,will he know what I mean without my having to know what SC4, SS or C24 is all about?
Tim (who's getting more confused by the minute)
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On Mon, 01 Dec 2003 19:13:32 +0000, Tim Nicholson

if you are going for this long span you will want a good graded wood,
these grades are based on various factors, and can be either visually (given BS4978) or machine graded (given BS EN 519). You can generally tell the grade just by looking at the wood (which is what the QP doing the grading does) going on the total knot content, their size and their distribution. Splits in the wood can count against the strength of a plank, a split along the grain does not count much against its overall strength, whereas a split traversing the width (partially or totally) will count considerably against. Machine grading is carried out by measuring the deflection of the wood versus weight applied.
Aldo grades should be based on the woods final usage e.g. wood for internal use should be graded as KD (kiln dried) or dry, and external wood as wet. Wood should be graded at the right moisture content for its intended purpose. however tanalised wood will be graded prior to tanalisation and will be very wet if sold shortly after being treated.
I am quite amazed sometimes though at what does actually get graded, and on quite a few occasions major faults in the timebers of 2x4 size can be shaken and snap quite easily
Ungraded (totally different from unsorted) can mean one of several things,
I genuninely hasn't been looked at and can be very good wood indeed.
however it now normally means that the person qualified for grading wouldn't want his personal stamp on that wood, as it really isn;t up to scratch.
Also something to look out for especially on 6m+ lengths of 9x3 or above is that it hasn;t been finger jointed (very fine teeth at about 5mm repeats and teeth depth of about 1cm) these can come in fully graded lengths, but i would err on the side of caution here if the wood is going to get wet and get wet often. I have seen these joints highly compromised if left in water for extended periods of time.....YMMV
i hope that this will answer your question a little bit more fully
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Nicholson wrote:

1kg = 9.81N (OK I know you shouldn't equate force and weight) 1kg = 2.2lbs 1m2 = 10.76ft2
So 0.25kN%0N%.48kgVlbs/m2=5.2lb/ft2
The normally assumed live load on a domestic floor is 1.5kN/2 or about 30lb/ft2
--
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wrote:

Damn that must be an old calculator, SC4 doesn't and hasn't existed for a long time.
SC4 (strength class) is equivalent to ss (special structural) or c24 grade
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Hi David
That may be true in engineering and architectural circles. But at grass roots level it is alive and well. Hasn't quite filtered down here yet.
The building regulations own tables stipulate SC4 and SC3 as do many of the books.
I was quoting form tables found at the Office of the Deputy Prime minister and from the book "Building regulations in brief" by Ray Tricker and published in 2003.
--
Danny Burns
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Hemmings wrote:

For all practical purposes, yes. The C24 (C=coniferous=softwood Dciduous=hardwood) is the Eurocode replacement classification for SC4 and defines the working stresses that can be used.
The GS/SS grading relates to the quality of timber (knots, slope of grain etc), and its strength will depend on its species. As it happens all the structural timber we use (i.e. northern European or North American) that is graded GS or SS falls into C16 or C24 but UK grown timber (IIRC) would fall into C14 or C22 - warmer climate = faster growing and less dense.
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wrote:

quite just as i posted yesterday
and its strength will depend on its species. As

Yes true, personally never seen wood stamped up like this. The market is totally saturated with the north european redwood, why ? easy it is better and cheaper than home grown. If you can get swedish over latvian then do so, it comes up much nicer; you have to turn over a lot of the latvian stuff, whereas the swedish you can more or less just take them as they come even for stud work)
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wrote:

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Danny Burns wrote:

Any chance of using bolts and making a braced girder type structure? I.e. a top and bottom rail, with vertical and diagonal struts bolted between...such a structure is far more resistant to deflection and thus far more suitable for long spans such as you have. IUn addition it will need to be restrained and made stiff horizintally, otherwise teh top spars will buckle under load. This is done by linking each side of the bridge with horizontal members, both straight and diagonal.
THis osrt of problem is usually given as an example in first year structural engineering courses - was on mine anyay - suggest that you find local uni dept and/or firm of structural engineers to rough out the calculations on absolute strength and deflection under load for a simple braced girder end supported beam.
If its for foot traffic only, a gut feeling says that you could probably build a decent box gorder structire out of 6x2 and get way with it. To carry farm vehicles over that span tho, I'd say steel is required or very substantial timbers - maybe 12" or more.
A couple od substanntial steel I beams might anyway be a simpler solution, with cross pieces welded betweeen..
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There is a very good design service here, try it and see what you get! (intended for others following this thread, I guess you've started already!)
http://www.arbordeck.co.uk/design.php

Ouch! that taxed my brain too much - try the group instead!
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