My name is Joel Foster, I am a student at Cork Institute of Technology in Cork, Ireland. I’m originally from Canada, but am here studying a BSc (hons) Architectural technology. As a requirement of my program I am writing a thesis on the ‘necessities of the hammer beam'.



Throughout my research I have found out the how and why, but lack the information on the typical joinery of the hammer beam and arched ribs spanning from the hammer post to the tie beam. My questions are:

1.
Are the arches typically cut/milled from a single timber, or are they constructed by joining two or more timbers to create the arch. If multiple timbers are used, what type of joinery connects them? - scarf joint?

2.
When the hammer post joins to the hammer beam what is the typical connection? would most simply do a mortise and tenon, or would you use a through tenon for decorative proposes?

Thank you,
Joel

Hi Joel,

I will do my best, and I am sure others that have built Hammer Trusses will join in...

Yes...

This is tricky one to answer at it depends on the truss design, and how it is facilitated. I usually try "book matching" both side of the truss assembly, but that is more out of traditions and aesthetics that engineering, though I believe the symmetry does add strength.

Scarfs, and splines are probably the most common, will see what others have to say on that.

I prefer a housed joint with through tenon and wedge.

Example:
http://www.logandtimberschool.com/courses/frame-bents.php

See Above.

Regards,

jay

I am still under the influence that a hammer beam truss is not a truss. I leaned this at one of the Heartwood classes years ago. The joints are hinge points and without substantial post or stone buttress the "truss" will not carry the roof load, the walls will spread, with larger buildings and time. Benson woodworking found this out first hand and added cables to their hammer beam trusses. It must be documented somewhere. Look into this for your project.

Hey Tim,

Good to bring that up for his research. Many contemporary examples being built in shops today would benefit from those tension cables, as many "hammer beam trusses," are not designed well enough (in reality) to endure over time. You can achieve a true HBT but you really must be familiar with this type of truss assembly, applied roof diaphragm loads and there tipping (over through) effect on the wall diaphragm.

Those that don't need a cable tie to be enduring are typically other types of trusses designed into a hammer beam "arch," which is really what we are talking about.

If you get the roof pitch steep enough, the timbers heavy enough, and the joinery designed applicably, you get a "hammer beamed arch."

Below is a good read, and as we progress, I am sure others will suggest more. It would be nice if we have a good bibliography on this subject by the end of the discussion. I would also be wonderful if Joel web publishes his paper.

Regards,

jay

Roof trusses pp 1006-1020; (but the good stuff starts on page 1013 for this conversation.)

The Architects' and Builders' Pocket-book: A Handbook for Architects, By Frank Eugene Kidder orig. 1885 14th ed 1916

http://books.google.com/books?id=e1swAAA...uss&f=false

And bump up and read page 998, if you can stand it, where a truss is defined. Hard to follow why the hammer beam truss can still be called a Truss. When it lacks longitudinal tensil strength. How does one describe Longitudinal Tensil Strength? And does a Hammer beam truss have it?

Thank you for all your help, I really appreciated it.

I have constructed a scaled model of a "typical" hammer beam truss, this Monday (18th November) I will be bringing it into the structural labs at my university to perform a full structural analysis on the individual components (tension/compression) and a study on how the force is transferred through the truss down to the corbels. when my research is complete on the traditional joinery I will build another test truss and perform the same test.

I will read your suggested text, and do more investigating into the joinery - possibly build a couple test joinery sections and perform similar tests in my research. I will most definitely provide you a copy of my thesis or web publish it when its complete. The thesis submission will be this coming June 2014. If you like to see the outcomes please let me know.

Thanks again,
Joel

Please consider having it published in our journal: Timber Framing.

I'm sure the editor would like to see it.

Jim Rogers

PS. you'd get paid for it as well.....

Hi Joel,

This is well trodden path with lots of emmotive discussion having taken place over the years on how exactly hammer beam roofs behave.

They can be quite long lived with Westminster hall roof now over 619 years old and Pilgrims hall in Winchester nearly a century earlier.

Ed Levin wrote quite a bit about the structural performance of these roofs published in Timber Framing as did William Harvey in the Modern Carpenter & Joiner (1920's) where he explains about building "unconnected" block models of Westminster Hall roof. Lyn Courtney and Robert Marks published some papers in Timber Framing and elsewhere plus Yun Shen Huang (one of Mark's students at Princeton) did his thesis modelling the behaviour of a Westminster Hall Truss. It's really worth while checking out "Timber as a Structural Material" edited by David Yeomans published by Ashton which includes a compendium on the structural performance of Westminster Hall roof. It's worth also checking out the drawings made by Deneux and Ostendorf and even earlier ones by Viollet-le-Duc. Recent publication on European Roofs by Patrick Hoffsummer include details on continental Hammer beam roofs. Raphael & Arthur Brandon published a book on Timber Roofs in late Victorian times on East Anglian church roofs many of which are of hammer beam construction.

The modern day plane frame analysis programmes should provide you with the answers that you need but as allways the challenge is to know how the various joints behave e.g pin, spring, moment connection and little practical experimental outcomes are published in this respect so that this could be an area worthy of focus in your thesis.

Don't be tempted overlook the small hammer beam roofs tucked away in non descript places like No 21, The Causeway, Steventon in Olde Berkshire plus Imberhorne Cottages in East Sussex.

Take care not to publish your thesis until after it has been marked as all thesis require to be original unpublished work.

Check your PM's.

Ken Hume

Excellent words Ken...good guidance to follow.