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Hospital Pendants Structural Calculation

Hospital Pendants Structural Calculation

Hospital Pendants Structural Calculation

(OP)
Hi,

I m asked to calculate the allowable load for a designed hospital pendant which needs to be mounted on the ceiling.
The company has given me a similar sample to take reference but I have a lot of steps which I don't understand, so sorry there may be a lot of questions I need to ask for...

First, at page 3, Spreading area = (560+2x90)x(311+2x90) = 740x491mm^2
I don't know where are those numbers come from?

And at page 4 about the Restoring moment about edge, I also don't understand the whole step, where 9.8 kN comes from and FS = 14>1.5. Does FS mean Factor of Safety?

And last at page 6, starting from Check Restoring Moment: 3 nos. of M10 HSL
It will be grateful if anyone could explain whole calculation steps.

Thank you for helping



RE: Hospital Pendants Structural Calculation

If you don't understand how to do the calculation on your own, let alone when you have a close example to follow you probably should not be doing this job... especially in a hospital for heavy overhead equipment.

FS typically means Factor of Safety but context within design calculations should be clear

RE: Hospital Pendants Structural Calculation

Spreading Area - the 560 is the width of the plate, the 90mm would make sense as the depth to reinforcement for a 140 mm slab ("d" for us ACI people), the 311 is slightly more than the compression stress width. I don't know what use it would be to determine the "average" applied compression stress on the slab unless it was to compare it to an allowable Dead or Live load design for the slab (the calc doesn't evaluate this stress). Even then it doesn't make sense since this compression is acting up and not down. If you need to check the slab, I would expect to see a 1-way and 2-way shear check and a slab moment check. I recommend looking for a "Point Load Distribution on slab" document for checking the slab.

Restoring Moment - the 9.8 kN is the tension capacity of the anchor. The (0.27 + 0.27) for the 3 anchors should be the moment arm from the anchor tension to the compression centroid (which its not). FS is as you said "Factor of Safety"

Further notes:
First, I am used to seeing 4 to 5 ft of space between the ceiling and the structural soffit above and would recommend dropping your support down to the recommended mounting height suggested by the equipment vendor. This has the added benefit of giving you lots of space to install a nice wide base to support the structure as well as include the lateral braces for the long drop height.
Second, the overturning moment can occur in any direction and, when oriented orthogonally to the plate, is probably not worst case.
Third, for a lightly loaded system such as the MMP90, consider a light gage metal channel framing system (ex. unistrut) - see attached.

RE: Hospital Pendants Structural Calculation

I'm assuming from the year in your username that you're pretty new at this. If you don't understand what's happening, take your best stab at it and then ask a senior guy in your office to work through it with you.

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