P1001 Unistrut Design for Ceiling Mounted 2-tons Cath Lab 1

[Manabat]

Hi Everyone,

Thanks in advance for your valuable time and feedback.

A bit of background: I am a junior engineer, fresh out of college, and have been given the opportunity to design a unistrut frame that will carry a ceiling mounted cauterization lab machine weighing 2-tons for a hospital (ref to Image 1 below for 3d concept of cath lab - yellow highlight).

Image 1 - 3D Concept of Cath Lab (Yellow Highlight)

That cath lab consists of a C-arm and 56 inch monitor that are movable and are attached to a rail system. According to the suppliers specs, I am supposed to specifically use a P1001 unistrut system(configuration is my choice) to connect the rail system of that Cath lab to the ceiling of the hospital wing set apart for this equipment. The image below shows the specific room of the hospital wing the machine is to be installed in.

Image 2 - Existing Site Picture

After my site visit late last year, I saw that the hospital wing in question was a single storey structure of concrete/masonry construction with a timber framed and corrugated profile tin/metal sheeting clad roof - essentially, the existing ceiling is incapable of carrying 2-tons of weight and that a separate steel frame would need to carry both the unistruts and the cath lab machine.

Unistruts are something that I have come across for the first time so I'm jumping off the deep end with this. My on-going research seems to suggest that I can configure them as trusses but complying with some of the manufacturers requirements - especially with the stiffness requirements, really befuddle me.

Here are some of the requirements for context:

Image 3 - Specs 1

Image 4 - Specs 2

Image 5 - Specs 3

Additionally, because the cath lab unit is one that has moveable members, the supplier also provided static and dynamic forces for the design (ref below). I'm still in the process of clarifying with them about the distribution of the forces.

Image 6 - Static Forces

Image 7 - Dynamic Forces

I tried to be as detailed as possible with this item of mine and I'd appreciate your advice on how I'd go about using them for this medical application.

Cheers!

 

[dik]

I'd be using a more substantial structure than unistrut.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Tomfh]

I’d be designed a structural steel frame to support it. There’s an expectation with this sort of medical gear that the supports won’t budge. If your unistrut flexes around as the machine moves around you’ll be hearing all about it.

 

[Aesur]

I agree with the other posts here, use a steel frame. Unistrut may technically be possible, however make sure you understand all the factors associated, from loading pattern, to reductions for holes in members, depending on type of hole etc.. connections can also be a bit tricky. If I were to provide a Unistrut frame for this, it would be supported by a new steel frame and connected often, relying on the Unistrut for adjustability of connections of equipment only.

I would anticipate you will see all those varying load distributions because these are typically designed for all those configurations and they may use any or all of those.

 

[WesternJeb]

I am doing the exact same project right now. Use a steel frame or it will be impossible to keep within the vibration tolerances and deflection limits.

 

[DaveAtkins]

I disagree with all of the responses here. The medical equipment is specifically designed to be attached to Unistrut, so that is what you need to do. As far as the roof deck being inadequate to support the Unistrut, you will need to add structural steel framing as required to provide adequate support for the Unistrut framing.

DaveAtkins

 

[trevorshiloh]

Right, but I would argue the unistrut is to be used as minimally as possible, only to provide the connections for the equipment. The rest of the structure should be steel.

 

[DaveAtkins]

Agreed.

DaveAtkins

 

[JedClampett]

Further, you're supporting a piece of equipment that costs, I don't know, $3,000,000 or $4,000,000, on a couple of thousand dollars' worth of steel. Make it stout. Unistrut is a fine product, but it is not a catch all.
We have typical details for pipe supports made of Unistrut. And since they're typicals, they get abused. It's pretty awesome looking at a 24-inch diameter steel pipe that has crushed a Unitstrut.

 

[WesternJeb]

DaveAtkins, that's what I get for not reading the entire thread. Yes, the equipment HAS to attach to a unistrut. I thought we were talking about the support for the unistrut itself.

 

[bones206]

Unistrut is commonly used for medical equipment supports. The moment of inertia for a P1001 beam is roughly the same as an L3x3x1/4 angle, for sake of comparison. If you keep the spans short, it can work fine.

Check this website for examples:

https://unistrutstore.com/unistrut-medical-equipment-supports

 

[bones206]

Attached is an example cath lab support from the above website link.

 

[JLNJ]

You can get the unistrut to work, at least for the parts which the equipment attaches to and runs along. Unistrut makes a bevy of different shapes. The forces are usually relatively small.

I've done a couple of these, including one which was trying to be hung from a roof. I told them that there was no way to meet the stiffness and deflection requirements without tearing things all the way back to the columns. They are looking for somewhere else as I type. It can be tough finding a spot since they won't want to demo a whole bay's worth of framing for a one-room modification.

Often, you can talk to the manufacturer about their stringent requirements and get them to back down a little. Or make the hospital aware of the possibilities if the floor above deflects under its own live load. You can only control what you can control. Sometimes it's "indemnify yourself, support from the girders, and hope for the best". Don't take responsibility for $4,000,000 of equipment for a $5000 fee.

A side note: It not unusual to run into manufacturers' requirements which just are not possible to meet.

 

[dold]

I have done pretty much this exact same project. We provided a steel structure that was supported by the walls entirely independent of the existing roof framing. Unistrut was welded directly to the new steel and provided only as a means of attaching the track system to the new steel.

Deflection controlled the design. Our C-arm was actually mounted on a track system so the C-arm could be moved around in the room in two directions. I think I modeled it in RISA 3D with a bunch of moving loads to envelope all configurations.

Like others have said, this is a multi-million dollar machine. Don't skimp on the steel.

Edit to add: what we ended up with looked a lot like bones206's link, except it was all hot rolled steel. Braced in both directions with diagonals to prevent movement in the horizontal plane.

 

[Manabat]

Hi Everyone!

Thanks for the really clear advice - it really has removed some of the doubts I was having regarding these unistruts.

And I wholeheartedly agree with you all on not skimping with the steel.

Much thanks again with your valuable feedback.

Cheers!

 

[Manabat]

P.S: Dold, Hi, probably a stupid question but I'm just curious on how you'd interpret the static and dynamic forces in Image 6 & 7 when modelling it for your steel frame in RISA 3D.

From what I can understand:
[ul]
[li]Forces P1 - P4 are directly my tension/compression forces derived from the weight of the C-arm and it's rotation; and,[/li]
[/ul]
[ul]
[li]I can get my lateral forces (that can act on the bottom flange of my steel frame) from my Mx, My & Mz.[/li]
[/ul]

The main question I had for the supplier was if there were specific locations/coordinates for forces P1-P4 (based on my aforementioned understanding of their forces). It's a bit difficult getting in touch with the supplier's technical guy at the moment as they still must be on leave.

I'm more of a SAP 2000/ETABS person but I'll definitely learn a thing or two from what you did. Also, do correct me if I mistook anything earlier.

Cheers!