seismic supports straddling building expansion joint

[CPBe]

Looking for some insight on how to accommodate building expansion in some seismic supports for rooftop ductwork.
Building expansion in 1 direction is one thing, but I'm unsure how to handle 2 directions. See sketch below:

Currently thinking some canvas duct when crossing the E-W expansion could work; since the seismic stands would be fixed on each side of the N-S expansion, would some slotted holes be sufficient to account for that expansion? What if only the NE quadrant moves both N & E? (Is that even a possibility?) Would some sort of slide plate need to be designed?
(Note that relocating the duct is not a possibility)

Any assistance is greatly appreciated.
Thank you!

 

[HTURKAK]

YOu did not supply a lot of information here. What about the range of expected differential movement of the buildings? How are the duct supports will be supported on the roof ? What is the roof finish ?
If the roof top layer is walkable gravel , i would prefer simple base plates under the supports and do not plan to fix to the roof slab. The base plates can slide freely as necessary. But check the total system for wind uplift.
Another point , if the building is not a lifeline bldg, any limited ductwork repair should not be big issue.
The following doc. may give some insight.

 

[CPBe]

All expansion joints are 4"
Duct is supported w/strut stands & periodic seismic/wind stands comprised of anchored pipe posts & horizontal channel members.
Roof finish is a PVC membrane over insulation; the plan for seismic/wind stands are (for now) to be anchored to a concrete slab on metal deck - see sketch below:

Duct is as large as 96x60 (+/-60 lbs/ft) & design wind loads for this hospital/ER are 120mph - uplift loads are substantial.
I understand base plates not fixed to the roof slab would allow everything to slide freely, but wouldn't that negate any seismic/wind protection?
Would it make sense to anchor a single post for seismic/wind loads & let the other slide about freely on top of the membrane?

 

[TRAK.Structural]

I would think the ducting should have specific joints that can accommodate the expected movement across the bldg exp joint where the duct is perp to the bldg joint.

I would avoid having the supports straddle the exp joint like shown in the middle of your plan layout. Can you use and inverted "L" shaped support that is only attached on one side of the bldg joint in these locations?

 

[HTURKAK]

All expansion joints are 4"

That is , the expected differential movement during seismic event would be less than 4 in. This amount is manageable with expansion joints.

Duct is as large as 96x60 (+/-60 lbs/ft) & design wind loads for this hospital/ER are 120mph - uplift loads are substantial.

In this case, i would prefer the use of expansion joints and some sliding supports under the duct and fix the legs to the roof slab.
I would suggest
- to look to the doc. ( Air and FLUE flue Gas Structural Design Committe - Structural Design of Air and Gas Ducts for Power Stations ( ASCE Publisher ) to get some insight for the behavior of large scale ducts.
- add two extra EJ in horizontal direction.

 

[CPBe]

@TRAK.Structural - Unfortunately, there's no re-locating the duct. (Believe me, that's the first question I asked!)
@HTURKAK - What/where do you mean 2 extra EJ in horizontal direction? (Flex/canvas duct in 2 additional locations?)
Would specifying any in the vertical direction help?
And should a single leg only be fixed to the slab? That way any twisting of the supports is avoided (?) - see updated sketches below:

Let me know your thoughts.
And I appreciate the feedback!

 

[HTURKAK]

What/where do you mean 2 extra EJ in horizontal direction? (Flex/canvas duct in 2 additional locations?)
Would specifying any in the vertical direction help?

I have drawn proposed extra 2 EJ location with thick blue lines but if you can provide slide plates as shown on the sketch, no need to extra EJ . Just provide flexible / EJ as your original post . I have shown with thick red lines.
Your ssecond set-up is OK.