TDF/TDC Joint Reinforcement - SMACNA 1995

[NEplantengineer]

Hello, wondering if anyone has run into the following/has any advice:
I've got a sheetmetal contractor ductwork standards submittal containing a reinforcement schedule for TDF joints. They want to use flat bar stock to increase the rating of the joints for larger duct/higher pressure class. I'm trying to see if it meets SMACNA 1995 standards (that is my base acceptance criteria). However, when I pick through the SMACNA book, all I find is a vague statement on page 1.64 that "Ratings in table 1-12 may be adjusted when combined with EI rated flat bar stock or members from Table 1-10."

What the heck is EI rated flat bar stock? Also, I thought that unless you know where the moment of intertia is referenced to, you can't just start adding I's willy-nilly?

Any ideas?

 

[CountOlaf]

I'm not sure either, but I have a copy of that SMACNA standard. It defines E1 on page 1.15 as the stiffness index which is the modulus of elasticity x a moment of inertia. On the Table 1-10 you referenced, it has E1 values at each reinforcing class: for instance at class F it lists E1 as 12.8 (x 10^5), so I suppose if you needed class F for a particular intermediate reinforcement, then you would have to calculate a combined moment of interia of the flat stock plus other "contributing elements of the connector" such as the duct wall, and other reinforcement--kind of like they tabulate for "combination sections" in the steel construction manual (although those in the steel manual are for more standard structural shapes shuch as a C channel butted against an angle). And then finally, as long as the calculated value of E1 was greater than the required E1 in the table, you'd have an acceptable joint.

To save you the calc's, perhaps you could ask the submitting contractor to provide the stiffness index with their proposed modification(s) to see if it complies.