Reciprocal Roof

[biffvernon]

Are there any examples of a reciprocal roof from before 1987?

 

[MdB]

For those (like me) that hadn't heard of one of these:

http://greenbuildingelements.com/2008/10/01/the-reciprocal-roof-beauty-strength-and-simplicity-in-a-roof-frame/

They look like a neat idea to me. I haven't seen anything quite like that before but it does remind me of a self supporting ceiling designed by somebody famous, x hundred years ago. Is that vague enough for you? The ceiling beams were all the same length and a fraction of the span covered. The centre four beams are in the same arrangement as the picture above and hence self supporting. I've tried to find a picture of this ceiling but can't remember enough about it to google for it.

 

[biffvernon]

Thanks MdB, but somebody famous, x hundred years ago is just a bit vague. As you may have read on the Green Building Elements website:

The history of the reciprocal roof seems clouded due to a lack of comprehensive information (a Google search for “reciprocal roof” or related terms will result in only a handful of actual buildings featuring the design, plus some other minimal historical information), but from what I gather, it was designed by Graham Brown in 1987, when the idea came to him from “out of nowhere”

It does seem strange that such a simple yet effective design should have such a short history.

 

[David Dyer]

There is a book about reciprocal roofs that does have some history in it, I've only done a search on the Amazon site that just gives snippits of information but the design would seem to go back to at least the 13th century in Japan.
http://www.amazon.com/Reciprocal-Frame-Architecture-Popovic-Larsen/dp/0750682639

David.

 

[MdB]

The same idea remembered from my scouting days:

This is how the roof / ceiling structure I half remember was made. More later if I can find something on it. It is really bugging me now.

 

[MdB]

Found it:

http://www.soue.org.uk/souenews/issue4/wallis.html

I can't find a picture of the ceiling I remember seeing but this is the technique by which it was made. You can see the squares which are the same as the hand hold above and are the same principle as a reciprocal roof with four beams. The application is different overall though.

 

[Craig]

What about American Indian Wigwam/Teepees?

 

[biffvernon]

No, that's not a reciprocal structure, and nor is the square short beams thing above or the boy scout grasp, which is more about grasping. Looks an interesting book, David. Will have to investigate Japan further.

 

[MdB]

Here is a four beam reciprocal structure I put together out of some square section I had to hand:

This is exactly the same as the hands and Wallis structure above apart from the fact that there are no cut outs / notches in it. In the Wallis structure, the notches are to allow it to sit flat and not to hold it together. Indeed, the joints need to be able to pivot so as to share the load properly. If the joints were to be fixed, the load on some of the beams would increase significantly.

If round beams are used to make a reciprocal structure, the friction between them needs to be high so as to ensure the structure doesn't collapse as the force on each beam pushes the beams outwards. If square beams are used, notches need to be cut into the beams to allow the neighbour to sit flat and to counteract some of the sideways force.

I also put together an eight beam structure which looks a little more useful as a roof:

 

[biffvernon]

This is exactly the same as the hands and Wallis structures

Absolutely right. I stand corrected. Nice pics - your models show the idea very well.

 

[MdB]

It is an interesting structure. Thanks for raising the subject.

 

[David Dyer]

Biff,
There are many more extracts from the same book on Google books.
http://books.google.com/books?id=3zp2hEozZ-oC&pg=PA7&lpg=PA7&dq=history+of+reciprocal+roof&source=bl&ots=H1q_U1MXwn&sig=WRwOr382ufOIlbpIWkcr6jTLDd0&hl=en&sa=X&oi=book_result&resnum=7&ct=result#PPA15,M1

David.

 

[Jon Maine]

It is an interesting structure. Thanks for raising the subject.

Nowt quite like raising an interesting roof structure

 

[MdB]

One downside of these things I thought of was that one failure of one part will bring the entire roof down - which would be unfortunate..

 

[Jon Maine]

On the 4 one it would on the 8 one it may not but certainly would drop some. I guess a point in case of choosing your timber well and keeping it dry.

 

[MdB]

I guess it depends on how big an overlap you have. This one looks like it has very little (if any overlap) so would have problems if there was a failure. The first picture at the top of the page, is a lot better though and should only drop a little as you say.

 

[biffvernon]

Last night at a party I met a man who's day job is making reciprocal roofs. You need to go to the right sort of parties. Here's his website

and some nice pictures