Manufacturing Facility - Dead vs Live Loads

[metalchair]

Good Morning All,

Just a quick question regarding how to consider loads from some permanent equipment in a manufacturing facility.

I am designing a 2nd floor mezzanine that is to be used to support heavy manufacturing equipment at a load of 250psf per ASCE 7 table 4.3-1. This is fairly straight-forward when considering gravity loads only. However, when calculating seismic loads and seismic weight, do I also include the weight of the permanent equipment (conveyors, etc.)? Or is that overly conservative, as the equipment is wrapped up into the 250psf live load?

I figure using the 250psf live load and also including the true weight of the equipment in the seismic weight calculation is going to cover all my bases, however, I am wondering if this is overly conservative.

Any help is greatly appreciated.

 

[DaveAtkins]

I think that is overly conservative. The 250 psf is a blanket uniform live load to account for uncertainty in the type of machinery which could be used.

I think you can use the actual weight of the equipment being installed as "W" for the seismic calculation. Or, to be more conservative, you could use 250 psf times the floor area as "W."

DaveAtkins

 

[metalchair]

DaveAtkins, thank you for the reply. I guess I was not super clear in my last point made. I would be using the 250psf live load as the live load in load combinations. But for seismic weight determination I would be using the usual dead loads added to the true weight of the equipment. I would not be including the 250psf live load in the seismic weight calculation.

Thanks again.

 

[SlideRuleEra]

metalchair - If the equipment will be securely anchored to the mezzanine, I would include it in seismic loading.
If not securely anchored, it's live load.

 

[metalchair]

SliderRuleEra, thanks for the reply. I am assuming you mean if it is adequately anchored to resist forces as per ASCE 7 chapter 13, correct? In any case, I appreciate the feedback.

 

[canwesteng]

Is the area used for storage? If not, none of the live load should be included. The 250psf live load will more so be needed during maintenance of the equipment where large loads can be placed on the floor, although it isn't always (or often) enough for this.

 

[SlideRuleEra]

metalchair - Yes,the equipment would need to be anchored so that it moves with the floor during an earthquake to be included in seismic loading.

If the equipment is not anchored, the floor will move (horizontally), but (ignoring friction) inertia will keep the equipment stationary... giving the appearance the equipment is "sliding around" on the floor. Keep in mind that during an earthquake it's the earth that is moving and taking with it only things that are anchored to the earth (like the mezzanine and things secured to it).

 

[Greenalleycat]

Tricky one. Given that it seems to be a generic mezzanine with a machine then put on it, I would be mindful of long-term potential for the area to be repurposed as storage

I think I would design for the maximum of the weight of the machine you know will be installed, and a generic storage load which would range from 5kPa to 10kPa here
Under our codes I would consider these to be live loads so a factor of 1.5 would be applied for gravity load ULS design
Under seismic loading I would check the machine weight with a factor of 1.0 ("long-term installed machinery, tare weight" as per code - effectively gravity load) but the storage case with a factor of 0.6 (our code's EQ combination factor for storage live loads)