Piggyback Scissor Truss Assessment

[Struct1206]

I was brought in to look at a 40+ year old building due to concerns with the roof framing. The roof framing consists of piggyback scissor trusses that span roughly 55 feet. My brief assessment revealed failed plate connections, bowed top chord members, trusses bowed out of plane and evidence of significant vertical deflection. My gut feeling is that the trusses weren't properly designed to begin with and probably need to be replaced entirely. However, I don't want to jump to that conclusion without considering the possibility of reinforcing these trusses in place. Are these trusses too far gone or is it possible to rehab something like this? Thoughts?

 

[Struct1206]

Another photo

 

[Struct1206]

One more...

 

[XR250]

Uh, yea, no fixing that

 

[bones206]

Looks like the main trusses needed lateral bracing at the top chord, below the piggyback truss bottom chord. Instead, they connected the piggybacks with scraps. My guess would be contractor neglected to install the bracing per design, but who knows.

Although it may be possible to reinforce/rehab, the cheaper route is probably a tear off and rebuild. If the roofing is old and in need of replacement anyways, that helps tilt the cost-benefit towards tear off and rebuild.

 

[jayrod12]

Agreed with the others, with that level of distress, and what appears to be lack of bracing, the remedial work will cost as much or more than just removing and replacing the entire roof framing with properly designed and installed trusses.

 

[SWComposites]

Would applying plywood sheathing on one side of the trusses, connecting the two levels of trusses, and bracing between the truss, be possible?

 

[bones206]

Coincidentally, I ended up in a scissor truss attic today and also saw some members bowing way out of plane. They were web compression members with no lateral bracing.

 

[RontheRedneck]

I have no doubt that the base truss required purlins on the flat top chord at 2' O.C. That's why they're buckling, and I'm sure it's why the trusses have excessive deflection in them.

It might be possible to fix them. The trusses would have to be jacked up, and the chords pulled back in line. And broken pieces repaired. Damaged plates would have to have gussets.

I think you'd have to number each truss and mark each joint with the type of repair required. It would be one hell of a lot of work.


I would never design a 55' truss with 2X4 chords. That might also be part of the reason the trusses are deflection.

If you get any more pictures, I'm curious what he pitch break joint looks like on the base trusses. Doesn't look like a web goes to the joint.

 

[lexpatrie]

So much liability to retain them. Let alone the computational effort and the field measurements.