Roundwood Engineering?

Is there any information out there that can be used to make sure a roof stays up?  Books?  Websites?

depends on the roof. reciprocal roof? center post supporting the rafters or a center post with a capital? I've seen masonry stoves used as center rafter support. Also, what's going on top of the roof? Living roof will carry more weight and require more support. Slope will factor into the load bearing needs too. You can find all sorts of advice once you answer some of these questions. As far as engineering equations... can't help.

I was thinking a gable roof with a living roof on top (6" thick compost), which will give a slope below 30 degrees.

What I am really looking for are numbers to plug into some equations.  The ASTM standards contain information on testing, but i have not read them.  I do not really want to spend the $34 for a couple page paper... but might have to.

How would you go about building a roof and making sure it stays up using the first paragraph information?

I haven't done a living roof but I know you would need some significant support for a 6" cover. I would look into using roundwood since it's much stronger than the milled equivalent. This site is a great resource - http://www.greenhomebuilding.com/

what I meant about the roundwood is - if you can find numbers for milled lumber, trusses etc., the dimensional equivalent in roundwood will definitely suffice. You have some variables with a living roof too - ability to retain moisture, snowfall...

Hopefully someone else will chime in b/c I worry way more about materials than numbers.

This site is worth a look if you are into using roundwood,

hope it is of some help

http://www.the-roundwood-timber-framing-co.ltd.uk/

Wow - Tks Freestyle.
Never heard of this term before.
I've been designing a "Cabin" I want to build and rent out.
Thinking of using "Roundwood" as a way of saving money.
I want to use it in the Sub Floor and Roof with the outside in a "log siding"
The Girders need to be hewed flat on top - I have plenty of woodworking tools
but still looking at how to go about the flattening . Knowing the term will help finding info.

Alright, I have been doing research. So far this is what I have . . .

There are many books on how to assemble a gable log roof. The Log Construction Manual does a good job explaining how to build a log home (including the roof), but I have not finished reading it yet. He suggests highering an engineering (that is what he does), but I am sure engineers are expensive. At the end of the book are pages of resources this guy, Mr. Chambers, uses. One book I am going to have to buy is Log Span Tables by Allan Mackie. It costs somewhere around $31 and can be found at the LogAssociation.org. This book should do the trick if you can calculate the loads on the roof for each member.

But that is a gable roof. What about Reciprocal Roofs? A fantastic idea which I can not figure out how to engineer! There is a book call Reciprocal Frame Architecture available at amazon.com for around $50 (yikes!) that seems to be a great book after looking at the online preview through google.com. Still, I haven't got it. Still doing internet research to get around that price tag. I did find a paper on reciprocal roof engineering, but it is hard to understand (I am trying to make sense of it)... here it is if you understand math really well. Systemic Behavior of Plane Reciprocal Frame Structures

Don't know if this would be of help, have a look

http://www.awc.org/pdf/STJR_2012.pdf

Also Here

http://www.uaf.edu/files/ces/publications-db/catalog/eeh/HCM-00752.pdf

or maybe this

http://www.awc.org/standards/wsdd.html

This is a great place to find out properties of different woods in North America.
Softwoods of North America
There is also one for hardwoods.
Very informative paper and a very helpful site on understand wood in general.

Those span tables from AWC.org could work as long as the log encloses the cut lumber shape (I think this is what Cactus Rex mentioned earlier) since roundwood is stronger that dimensional lumber. Not the most material efficient, but it would work!

Sadly those span tables www.uaf.edu/et cetera... are only for trees in Alaska. I am not in Alaska. Otherwise those would work.

I got Ben Laws new book Roundwood Timber Framing (I believe it is called) but have not found anything on engineering . . .
He did give reference to a paper that went into the structural properties of wood. Mabye I can dig that out of my computer files later.
Good book though. He really builds those buildings natural. No nails. He just uses wood oak pegs help hold the roundwood together. Mostly the fancy mortise and tenon joints to the work. The guy is amazing. The Log Construction Manual wips out the chainsaws and such Still, if you get the general idea from the book I think an axe can work.

Okay, back to research . . .

Mike Ohler's $50 and up home book has some engineering in it.

The page with the chart on it happens to be in the amazon free preview....

would this be of use?

http://www.cps.gov.on.ca/english/plans/E9000/9311/M-9311L.pdf

I am not an engineer, but I like to build and I prefer them to be safe, so what I do is apply a little logic to my designs.

In the case of round wood it is pretty easy to find strength formulas by converting the round logs to beams. Lets say you want to span a 12 area with a 10 inch diameter White Spruce log; is it up to the task?

Well if we were to look at the weakest point of the log, the small end, and draw a square, we would most likely be able to get a 8" square box. Now 8 inch timber load bearing tables are easy to find, and it shows that an 8 inch beam with multiple point load can hold 4500 pounds for a 12 foot span. That is quite a lot.

Now the real world test.

I know for instance, that my bulldozer weighs 10,200 pounds. Being on tracks it would be a multiple point load, and so while I probably could cut (2) 12 foot long 10" logs and safely cross a 12 foot stream, for extra safety I might reduce the stream crossing to only 10 feet, just to be sure.

That gives me a quick, real world determination of how much the logs I am using can support. From that I can reduce my spans, or increase my logs diameter. Now I used my bulldozer as an example, but it could be any known weight, like your ATV, your car, etc.

I know a structural engineer might balk at this, but they are paid to design structures to hold certain loads at the cheapest possible costs, where as we are just trying to ensure we build things safe enough with the materials at hand. We don't have to over-think things here.