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Buddy Showalter,

Glad that you brought up the topic of wood connectors on the list.

In spite of what tests have shown, the tabulated values for shear plates and 
split ring connectors are wholly inadequate for long term (25-30+ years) 
loading, particularly in hot, dry climates (can't speak for other climates) 
and are incapable of resisting the design dead load.  In dismantling a split 
ring connected truss, the wood within the split ring remained in the split 
ring, thereby not contributing to any strength of the connector.  In 
addition, in tension members, wood shears off the end of the member the width 
of the split ring/shear plate as it would if it was chiseled off.

This is not an isolated instance.  End, edge and center-to-center spacing 
were in compliance with code requirements.  It happens time and time again!  
If AF&PA wants to fund research in the properties and strength of wood 
trusses that were constructed in 1955 and started failing in 1981, I have 
knowledge of a roof that is finally going to be replaced and can put you in 
contact with the appropriate parties.

I would be very hesitant to use even 50% of the tabulated values in designing 
split ring/shear plate connections and recommend that the tabulated values be 
reduced at least that amount.

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

>>A new Technical Report developed by AF&PA's American Wood Council is 
available in PDF format on the awc website at
http://www.awc.org/publications/tr12/

It is titled "General Dowel Equations for Calculating Lateral Connection
Values:Technical Report 12. The Introduction reads as follows:

The yield limit equations specified in the "National Design SpecificationR
(NDSR) for Wood Construction" (AF&PA, 1997) for bolt, lag screw, wood screw,
nail, spike and drift pin connections represent a mechanics-based approach for
connection design. This approach, which was incorporated in the "NDS for Wood
Construction" in 1991, permits the designer to determine effects of member
thickness, member strength, fastener size, and fastener strength on lateral
connection values for the majority of connections found in wood construction.
This report covers calculation of lateral values for single dowel type
fastener
connections using
a generalized and expanded form of the NDS yield limit equations. These
general
dowel equations apply to NDS connection conditions, but also permit rational
and
consistent treatment of gaps and fastener moment resistance, and consideration
of various connection limit states. General information is provided in Part I
of
this report. Part II contains example problems and Part III provides equation
derivations.

Questions can be directed to awcinfo(--nospam--at)afandpa.org or by calling the AWC
Helpdesk
at 800-AWC-AFPA (292-2372).<<