[TheForge] Timber Straps

Fri Oct 25 09:43:00 2002

You know- I thought more about this and the shrinkage and wood loss issues when using bolted straps. I then went and looked at my Greene and Greene book (American Arts and Crafts architects) and felt reassured when all of those issues could be addressed with their solution of using wrap around straps using wedge joinery. Several of their 'Ultimate Bungalows' of the California elite had Japanese influenced timber frames constructed as such.
I went as far to make some prototypes myself and am amazed at their holding capacity. No bolt holes to drill and if there is shrinkage, tighten them up.
This may not be a solution for everything, although it would represent a truly blacksmithed product with no welds, no holes and beautiful joinery.

Steve Howell
Seattle

-----Original Message-----
From: Walter L. Mullett [mailto:[email protected]]
Sent: Friday, October 25, 2002 4:57 AM
To: [email protected]
Subject: Re: [TheForge] Re: (no subject) Timber Straps

Wood connectors are hard to design.  When I took my wood design course in
college, we used to say wood structural design "...depended on rather or not
it was Thursday and if it was raining". There are a lot of variables and
then when you account for all you can think of, mother nature puts a knot
somewhere.

If this is a commercial building, let someone else design the connectors.
If it's a house with small spans, Ralph's rules may work.  Wood usually has
what we call a "running" factor.  You hear it crack and you have time to run
before it falls.  Concrete, steel and steel connectors don't give you that
option.

BTW:  A lot of people don't understand that more is not always better.
There are instances where more of something in one place can overload
something else and cause a failure.  Wit connectors in bolts, more bolts
cause less wood.  If you don't know or don't have experience, let someone
look at the specifics who does.

Walt
-----Original Message-----
From: Joe Chadwick <[email protected]>
To: [email protected] <[email protected]>
Date: Thursday, October 24, 2002 2:43 PM
Subject: [TheForge] Re: (no subject) Timber Straps

>Ray-
>
>If there are engineer's design drawings, this could be a cinch. Cut, punch,
>weld, finish.
>
>If the builder just gave you a couple of his own sketches beware.
>Contemporary timber frames are frequently constructed with members having
>higher-than optimum moisture content. As the wood shrinks, extra stress is
>put on the bolt patterns in the wood, simple bearing sometimes goes away,
>and lots of unintended force vectors convene at joints never designed for
>the load. So the thickness of the gusset, the diameter of the bolt and the
>pattern of the bolt need to be figured together. Most of the time, the
>number of bolts needed to transmit a load to the wood will  remove so much
>of the wood that there is no capacity left in the member. There are
>however, a few styles of  "shear" connectors that can be bought or made
>depending on the  look of the joint.
>
>When I worked on coal-breakers (collieries) in my lost youth, gussets and
>straps usually started at 1/2". Granted, corrosion was a consideration, but
>later in school, the math proved out. Gravity load is only part of the
>picture, and a small part too. Wind loads, and the resulting stress
>reversals are spooky, especially since there is little in the way of
>redundancy in timber frames. I also don't know if your codes require
>seismic design for houses.
>I'm not trying to sound whiny. Like your contractor, everybody wants to
>shed job-costs and liability. Even if you (or whomever eventually does make
>these) hired an engineer to design the joints, that team holds more
>liability than if one were simply fabricating.
>
>Jeeze. Now that I took all the fun out of that job, I better get back to
>feeding the fire in the boiler of the bureaucracy.
>
>
>_______________________________________________
>http://mailman.qth.net/mailman/listinfo/theforge
>theforge mail list group photo site is
>http://www.photoaccess.com
>Login:  [email protected]
>password:  anvil
>___________
>
>

_______________________________________________
http://mailman.qth.net/mailman/listinfo/theforge
theforge mail list group photo site is
http://www.photoaccess.com
Login:  [email protected]
password:  anvil
___________

--- StripMime Report -- processed MIME parts ---
multipart/alternative
  text/plain (text body -- kept)
  text/html
The reason this message is shown is because the post was in HTML
or had an attachment. Attachments are not allowed.
Please post in Plain-Text only.---