Why is a multi-tier duct trapeze twisting out of square?
2nd YearTrapeze / Multi-Tier SupportsYELLOW · Check First
An off-center lower duct can twist the rods and strut. Rebalance the load or add an approved support rod on the heavy side.
Answer
A two-tier trapeze needs the load carried inside the rod span. If one line hangs far off to one side, the whole assembly becomes a lever.
Check the load center, rod plumb, strut rotation, and duct clearances. Recovery may be re-centering the lower duct, adding a third rod, splitting the support, or building a separate trapeze.
Field checks
- Check rod plumb and whether the strut is rolling.
- Confirm duct weight is centered within the rod span.
- Look for off-center hangers pulling the run sideways.
- Add support only by approved hanger detail.
- Re-level both tiers after correction.
Ask foreman
The two-tier trapeze at [location] is twisting because the lower duct is off-center. I checked the rod plumb and load side. Do you want it centered, split, or a third rod added?
Do not do this
Do not let a cantilevered duct hang off one side of a trapeze and twist the rods.
Why this matters
Eccentric loads fatigue rods, loosen anchors, and pull duct lines out of alignment.
Final direction still comes from approved drawings, specs, manufacturer instructions, employer policy, foreman/detailer direction, structural/seismic details, and AHJ/code requirements.