Sag Rods 1

[vmirat]

A contractor installed a new HVAC unit in an existing building, which hangs from the inside roof structure. The roof structure has horizontal cross bracing and each set of cross braces has a sag rod in the middle. The cross bracing bay size is 16'x16'. The new HVAC unit will prevent re-installation of the sag rod for this cross bracing. The cross bracing is L3x3x1/4 connected to the bottom chord of the open web steel joists.

At what point do members need sag rods? I'm thinking of ignoring this sag rod instead of trying to attach something to the bottom of the HVAC unit.

 

[vmirat]

I agree with hokie66 (I can't believe I'm agreeing with a VPI grad! wink, wink).

The other problem with this situation is that the HVAC unit is 6 inches lower than the plane of the cross bracing. The contractor wants to add stubs at the connection points to lower the cross bracing. This is one of those projects!

 

[hokie66]

Lowering the bracing sounds like a bad idea, typical of a contractor. Can you install bracing in another bay to accomplish the same thing? A Keydet should be able to find an innovative way to foil a contractor.

 

[vmirat]

In the immortal words of Kahn from Star Trek II, "He tasks me....".

I'm actually checking to see if the building is overdesigned as it is. My gut feeling is that the amount of cross bracing is overkill, and I may be able to leave it out altogether. The whole sag rod thing was really more of an academic discussion for my own edification. I agree that lowering the bracing creates a whole other problem of load path. I would like to string up the mechanical engineer that let them put this stupid HVAC unit in the first place, but he's a friend of mine, so I'm being lenient.