Structural Strength of Wild Cherry

[Gnarlyoak]

Any budding DIY self-builders out there who use natural materials, who can possibly help with this conundrum.

 

Got myself involved with a chap who is planning to build an eco building using clay plastered straw bales and various other recycled bits and bobs and timber. He is struggling to acquire a suitable 10m stem to use as a roof truss beam, which will run diagonally (corner to corner) across the bale walls and support the roof which will be layed with soil and plants to create a green eco-roof.

 

There is a mature Wild Cherry (Prunus avium) on site with a large straight secondary stem and he has asked me if this could be removed and used as the beam. Now I'm clueless as to the structural integrity of wild cherry wood used for construction in this way. The idea is to use it green and in the round, the diameter of the stem along its length, is 26cm at the base, graduating evenly to 15cm at the 10m mark.

 

He is unable to givem me an estimate of how much weight the beam will ultimately have to bear, but he did give me some idea of material volumes. Timber weight 61m3 Soil weight 2m3.

 

Anyone have any ideas as to wether the stem as described would be a suitable candidate to support the proposed roof, or is he barking up the wrong tree and creating a recipe for disaster?

[skyhuck]

You will need him to KNOW the weight the timber will be carrying, without those figures theres no way he will comply with building regs.

 

Remember it will need to be strong enough to still carry the weight even after being weakened by fire.

[Ian C]

You need a structual engineer in to do the workings out.

[slippery]

plenty of supports are the answer, timber has incredible crush resitance, you could do it with a 3x 2 if you ,had enough supports

[slippery]

but yeah, sorry , you need a structural engineer, i know a very good one if you get stuck

[Tom D]

In the old days when technical caluculations and building regs didn,t exist they used really massive oversized beams just to be on the safe side. Beams have got steadily thinner over the years to the point now where they are certified C16 or whatever it is, and are really thin because they have been carefully calculated to be exactly strong enough and no more. All you need to do is ask an engineer to spec the design in regular C16 wood and then double the thickness just to be sure, that should keep the building regs happy:001_smile:

[wills-mill]

10m unsupported is a biiiiiiiiig distance unsupported in timber..... regardless of species I think that's a no-no without several supporting posts.

 

 

We did the milling for this building-

Under the coppiced chestnut tree - Timber Building

and the fairly round and even 300 down to 200mm sweet chestnut poles had to be sawn through the centre and bolted back together with a steel flitch plate through the middle to stiffen them. And that was for a roughly 7m span.

 

You can see the steel in the photos at the bottom of this page

IStructE - Structural Awards 2008

 

Engineer time I think......!

Edited November 8, 2009 by wills-mill
adding a bit!

[wills-mill]

In the old days when technical caluculations and building regs didn,t exist they used really massive oversized beams just to be on the safe side. Beams have got steadily thinner over the years to the point now where they are certified C16 or whatever it is, and are really thin because they have been carefully calculated to be exactly strong enough and no more. All you need to do is ask an engineer to spec the design in regular C16 wood and then double the thickness just to be sure, that should keep the building regs happy:001_smile:

 

Green timber in the round is quite different to C16 which is based on actual strength grade test of samples. Technically you should get plenty of strength as none of the fibres have been severed, but engineers will also downgrade the timber as you may have unseen faults.

 

Cherry also tends to crack and spiral quite badly along the grain.

 

Try the architects and engineers that Steve used- Nye Saunders and Thomasons. They understand the issues of round timber and may be able to give you a quick yes or no at first Good luck!