Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

RE: Split ring failure

[Subject Prev][Subject Next][Thread Prev][Thread Next]
I recalled that this topic had come up previously, but, unfortunately, the person perhaps most knowledgeable, Roger Turk, has passed away.  Fortunately, he contributed some of his observations to this list.  I did a quick google search on {"roger turk" wood connection failure} and found this gem, among others.  I think it answers some of your questions directly. 
 
I had the opportunity to work with Roger on the repair of a failed bowstring truss several years ago (though it was not constructed with split ring connections).  If I recall correctly, one of Roger's concerns during the repair design was accounting for the redistribution of stresses that occurred during the component failures.  Something else to think about...
 
Good luck,
Brian
 
 
  • To: seaint(--nospam--at)seaint.org
  • Subject: Split Rings
  • From: Roger Turk <73527.1356(--nospam--at)compuserve.com>
  • Date: Wed, 26 Dec 2001 18:30:31 -0500
  • Content-disposition: inline
  • Content-transfer-encoding: 7bit
  • Content-type: text/plain; charset=us-ascii
  • Error-to: <seaint-ad(--nospam--at)seaint.org>
  • Organization: http://www.seaint.org
  • Owner: <seaint-ad(--nospam--at)seaint.org>
  • Reply-to: <seaint(--nospam--at)seaint.org>
  • Sender: Roger Turk <73527.1356(--nospam--at)compuserve.com>
  • Unsubscribe: http://www.seaint.org/seaintremove.asp?lstname=seaint

 
Keith, I would be very careful designing using split ring connectors. I have seen several failures of wood trusses that were approximately 30 years old where the split ring sheared the wood off the ends of highly loaded diagonal members. (Secondary failures gave the impression of failure due to twisting of the joints, but the twisting was the result of failure of one of the trusses having the split ring shear off the end of a diagonal.) The trusses were not overloaded, not subjected to snow loads (Tucson, Arizona), and occurred when no live load was present. Analysis of the truss under the code in existence when it was designed and the then current code showed that the truss should have been adequate for dead plus live loads. Dismantling a truss that had not failed revealed a plug of wood remaining within a split ring, i.e., separated from the wood member, therefore that area did not contribute to the strength of the connection. Were I to design a split ring connection, I would use only 1/2 of the tabulated values in the NDS (if I would use that much). A. Roger Turk, P.E.(Structural) Tucson, Arizona


From: Rich Lewis [mailto:sea(--nospam--at)lewisengineering.com]
Sent: Sunday, January 30, 2005 8:59 PM
To: seaint(--nospam--at)seaint.org
Subject: Split ring failure

I had a brief look at some roof trusses that were field fabricated some time around 1960.  I think they were split ring connections, although I'm not 100% positive about that.  I done some research on them and I'm going back for a second look.  I wanted to get some information from some of you who may have experience with split ring repair.  The trusses have started to fail.  The bolts are failing in shear at the end of the lumber.  The wood has sheared at the bolt hole with 2 shear planes the diameter of the bolt between the bolt hole and the end of the lumber.  A "plug" of wood is sliding out the end.  The bolt is ½" diameter.  I didn't measure the ring size yet.  The connection is a single shear type connection with one split ring.

 

Is this a common mode of failure for a split ring connection?  What are the recommended methods of repair?  I was considering using lag screws to replace the split ring but the shear value of the lag screws is not sufficient in the quantity I could fit on the lumber.  If I lagged around the split ring to compress the lumber together where the ½" bolt failed would that help reinforce the original split ring design?  Are there any published studies on repairing split ring connections?

 

Thanks.

 

 

Rich Lewis

Lewis Engineering