[TheForge] Re: (no subject) Timber Straps

Fri Oct 25 08:07:01 2002

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
>___________
>
>