What timber for bridge supports?

[Ian Leach]

I'm hurt you didn't recognize it was a swan , the man is smaller as he's further away walking toward us over the bridge. Thought that was obvious ????????

[sandspider]

Apologies, I see it now!

[Ian Leach]

......

[mixedangased]

Where do you get ducks bigger than a man?!!

 

duckland

[si36]

(Not sure if this is the right forum for this one, so if not can mod please move it to it's rightful place?)

 

I've been asked to quote for building and installing a bridge across a smallish pond to link the bank with an island. Only ones I've done before are relatively short (single) span, around 14–15 feet, so haven't needed a support in the centre. This one is around 30 feet, so will need a central support of some kind. The pond is clay lined but the owner doesn't know how deep the clay goes, so isn't keen on driving pilings in. I thought if I had the supports sitting on a flat base, akin to an inverted pi-shape, this should spread the weight and not sink into the base too much. In this part of the pond the water's only around 2-3 feet deep. (Or at least that's what he's said. Not got the chest-waders out yet!) Not sure how firm the base is, but it ought to be pretty good.

 

What do people think?

1. will this approach work? can you suggest a better solution?

2. would it require more than 1 pair of supports?

3. what would be the best wood to use, both for the supports and also the bridge itself?

 

Thoughts and suggestions welcome.

 

There is no reason the bridge will need supports in middle the largest bridge we have done unsupported is 85 feet, made of larch poles cut from Wales and transported to Hampshire to span the river avon near ringwood.

 

For A 30 foot bridge we would have a beam of at least 12 inch depth. 3 of them but that's just the specs for a bridge on a highway, we have to work to strict guidelines. We get our beams from sydenhams timber as they are stressed tested

[Copford sawmill sussex]

We have supplied both larch and oak to span widths greater than this, as long as the timber is sound and man enough most woods should be fine. If you can get away without using a center support the end product will look nicer.

[thewoodwizard]

Gabion baskets, normaly used for inbankments, you could put them in so they sit just above water level then wood

[thewoodwizard]

Gabion baskets, normaly used for inbankments, you could put them in so they sit just above water level then wood

[Badgerland]

Thanks for all your advice guys.

 

Thought greenheart might be the way to go, but as I've never used it before wanted to get other alternatives. I understand it's a tad 'harsh' on tools!?

 

The top of the bridge will be a mixture of green oak and sweet chestnut, so if I was to use oak for the supports instead do you think it might be a viable alternative? I'm considering 2 pairs of supports so would probably use 6" x 6" uprights or even 8" x 8"s. Reckon that would be durable enough?

 

I had thought of a single span but everything will have to be manhandled into place (and that means me and my mate). I don't mind a challenge but the thought of getting the 30 ft+ 12" x 3" lengths to site then getting them across to island doesn't fill me with delight.

 

Other advantage of using shorter spans means I can raise the middle span and add a little height/shape to the bridge. The surrounding area to the pond/lake is very flat, with very few points of visual interest, so getting a little shape into it might be a good selling point to the customer. Although its a practical structure to link the island its main purpose will be a focal point in the garden. (And his son's getting married in the grounds next year so no doubt it'll feature in the wedding photo's. Needless to say it's got to be right.)

 

Having said that I do like the idea of a gabion filled with stone, but as the pond/lake is already filled with the wet stuff it could be a bit of a bugger filling it and getting it level! Maybe for the next one eh?