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Split Ring Trusses and Epoxy Repair

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Mike,

Split ring information can be found in the NDS under Timber Connectors.  The 
timber text that I have, "Modern Timber Design," by Hansen, does discuss 
design of split ring connectors.  However, based on failures that I have 
seen, I would be reluctant to use even one-half the tabulated allowable 
forces in the tables.  Split ring failures that I have seen have had the wood 
shear off the end of tension members as would happen if someone chiseled the 
wood off the depth of the split ring.  Failures occurred under dead load 
alone and at widely separated locations in a shopping center.

Disassembling a truss that had not failed showed one split ring contained the 
wood plug from a member.  This wood plug is supposed remain connected to the 
member and to be part of the force resisting system.  Obviously, in this 
case, it did not contribute anything to the strength of the joint.  If a 
split occurs thru the bolt hole, then obviously the strength contributed by 
the bolt bearing on the wood is no longer present either.

Trusses that I examined which were constructed in 1955 were well designed 
and well constructed trusses, with proper center-to-center spacing, end and 
edge distances.  Occasional members had "test" written on them in lumber 
crayon.  Failures started in about 1983 and continued from then on.  In 
1985, an unrepairable failure occurred over a women's clothing store.  In 
1987, a truss failed over a drug store at the opposite end of the shopping 
center.  In about 1990, the roof over most of the shopping center, except 
over a supermarket, was replaced.  Trusses continued to fail over the 
supermarket and finally the supermarket moved out earlier this year.

As far as using epoxy to repair your trusses, I can't really comment on 
that.  Several papers have been written by Richard Avent, a professor at, I 
believe, at a university in the southeast, on that subject.  One thing that 
should be kept in mind is that glue has its greatest strength in shear and 
has no predictable strength in tension.

Hope this helps.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Mike Zaitz wrote:

>>hello,

I have a project where we inspected some built up split ring trusses.  In
most of the web members the ends are split, some as much as 1/4" wide.
First, where can I get information on split rings?  Second, are the split
rings still effective  even with the splits through the end of the member?
Last, has anyone heard of using an adhesive to repair this kind of problem
and where could I get some information on it?

Thanks,

Mike zaitz<<