Stockyard 2nd July 2007, 08:48 PM Hello, I am building a bridge over a creek on our property and am wanting advice on what timber I should use. I have laid two treated hardwood telegraph poles across the span of the creek (11 metres) which are approx. 1.4mtrs apart. I am unsure which way to go for the treads though - whether to use Treated Pine or Hardwood.
I am leaning towards TP because it is much easier to work with. I was thinking of using 140 x 45 spaced about 10mm apart.
My question is will the TP last as long as hardwood? Will one bow or twist worse than the other? I intend to leave the treads as they are as it will be a huge job to maintain with timber preservatives etc.
By the way, the bridge is only for foot traffic and to drive a ride-on mower across. Any advice would be much appreciated.
echnidna 2nd July 2007, 09:29 PM Hardwood is heaps stronger than TP.
I don't think 45mm is thick enough for a 1400mm span,
I think you need 70mm for that span.
Hopefully someone with span tables can comment.
les88 2nd July 2007, 09:45 PM treated pine will warp and twist especially in hot conditions Hardwood wood be my choice
:2tsup:
rhancock 2nd July 2007, 10:19 PM Best site ever for building bridges - www.outdoorstructures.com.au (http://www.outdoorstructures.com.au)
They have brochures on on bridges, timbers, maintenance all sorts of stuff.
Pops 3rd July 2007, 01:45 PM Hi Stockyard,
Never built a bridge myself but I did investigate a T&G floor with 1.5 metre span for the joists. The timber supply company got their engineer to look up some tables, (their own tables not Aust. Stds.) and advised me that 45mm thick T&G pine would span 1,5 metres. BUT this was for a T&G floor not individual planks.
So I would say you are on the edge of the strength limit, and as others have said it will be more prone to warping. All the new marina walkways I have seen used hardwood, 45mmm + thick.
Sorry no great help I am, just opinion, you are likely to get longer life and strenght from hardwood.
Cheers
Pops
Bleedin Thumb 3rd July 2007, 03:23 PM 1.4 m is a HUGE span... as Bob Thomas says check you span tables, they're going to be close to sleeper size over that distance. Whatever the dimension of the timber I would be looking ar TP as you have a lot of heavy lifting ahead of you.
Stockyard 4th July 2007, 12:34 AM Thanks everyone for the advice. Sounds like the hardwood will last longer. Should I get treated HWD? I thought this would be easier than having to paint a timber preservative on all the treads myself. If so does this come in 6mtr lengths like TP does. I have only ever seen it in sleeper sizes ie 2.4mtrs - which would make for massive wastage when my treads are to be about 1.5mtr.
Thanks Richard, I checked out that outdoor structures site - heaps of info on there
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