Duct Fabrication - SMACNA DCS - Transverse Joint - Standing S T12 1

[IBechir]

With reference to the subject title, I did not understand a passage in the SMACNA Duct Construction Standard Metal and Flexible, Second Edition, page 1.63:

Joint [...] T-12, STANDING S: When using S on all four sides, fasten the slip to the duct [...] at 12" (305 mm) maximum intervals.​

I thought the Standing-S slip/drive has the same length as the duct side it is joining so I did not understand what was meant by maximum intervals. So if the duct side, to be joined with a Standing-S, is longer than 305mm I have to make more than one cleat?

Can someone please explain?

 

[berkshire]

S bar on all 4 sides is normally used where the duct has to break away such as at a fire damper through a fire wall.
If you use S joints on all four sides for anything else , it has to be treated as a slip joint, with fasteners screwed or riveted through it to retain the duct. Otherwise the method is S bar on two sides opposite and drive lock on the other two sides.
B.E.

You are judged not by what you know, but by what you can do.

 

[IBechir]

Thanks berkshire but the phrase maximum intervals is referring to what exactly- the side length?

 

[berkshire]

As far as I know , it means exactly what it says , I interpret this as the maximum spacing between fasteners, so if you have a 48" wide duct you would need at least 4 fasteners in that side.
B.E.

You are judged not by what you know, but by what you can do.

 

[IBechir]

Yes I get it. If fasteners are not used and all four sides are using S then it will be a slip-joint and it can be dislocated. The intervals are like the ones shown in Fig 1-11 of the same standard. Thank you berkshire.