Truss Plate Stress vs Member stress

[AdamJSR]

Just got done analyzing a metal plate connected truss. By the grade of lumber used (S-P-F 1650f 1.5E) the member combined stresses are very low (around .3-.4) with my assumed loads (around 60psf total). I don't have a good way to analyze the metal plates. Ideas? I can't imagine they would engineer the TC a 2x6 (2x4 BC) and make the plates so very weak as to be weaker as the 0.4 CSI??

 

[charliealphabravo]

I would contact the engineers at Mitek or Alpine for plate analysis questions. They have been pretty accessible to me in the past.

 

[AdamJSR]

Do you more experienced members have any tricks on how to determine who manufactured trusses you might be trying to analyze?

Most I see barely have grade stamps on them.

 

[charliealphabravo]

Alpine and Mitek will recognize photographs of their own plates. If the plates are older they might be from a defunct company and then you are SOL. Actually even in those cases the engineer's at Alpine and Mitek might be helpful to a point. Some of those guys have been around a long time and may have even worked for some of the other companies.

You are facing a common and old problem as you will see if you do a search on eng-tips. Proprietary truss plates are a problem and I have not seen a clear solution. Mostly it comes down to making some assumptions about the performance of the plates...basically ignoring them for the purposes of member force determinations. This is not always conservative however, since the plates induce moment in the members. Also indeterminate 3-point bearing, cantilever, and vaulted/scissor trusses are highly sensitive to truss stiffness and not being able to model the plates appropriately only adds to the sensitivity.