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latinoguy (Mechanical) (OP)
18 Feb 09 19:49
Hi all. I am trying to develop a procurement specification for large CT systems, and am stumped in how to specify the requirements for floor loading. Because the CT systems are going into a variety of different facilities and floor types, I would like to specify a maximum floor load, such that not only can the facility be prepared accordingly, but more importantly to ensure interchangeability among a number of pre-qualified CT systems (i.e. if one goes down, we can replace with a similar pre-qualified one from another manufacturer). My question is: what basic parameters should I be using to specify maximum floor loads?

I do know the weight of all the commercial CT systems being evaluated (range 5000 to 20000 lbs), but I hardly think specifying a maximum CT system weight is enough. I can also guess on a maximum pressure load (3500 psi?), since most facilities are concrete slab, but that is attacking the problem from the facility side, which I probably cannot characterize adequately (i.e. some facility installations may be raised flooring). If most limiting case is a raised floor, should I specify a maximum point load per raised panel (2 ft x 2 ft)?

In any case, for floor static bearing pressure only, are there any structural engineers out there that can suggest an approach? Thanks
 
Helpful Member!  BigInch (Petroleum)
19 Feb 09 17:34
First, what is a "CT" system?

I would think 3500 psi is very very high, as a lot of concrete mixes would not take that kind of pressure.

You could try specifying a maximum load in lbs per square foot, such as 250 psf.

 

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

tygerdawg (Mechanical)
20 Feb 09 7:04
I've seen manufacturing facilities specified with 5000 psi concrete of (some number) inches thick.  This was done to provide support for the footpad point loading from heavy machinery.

Also I would suspect you could specify that the floor must support a "kazillion pound load distributed over and area of X square feet with Y inches maximum deflection measured from Z".  This would probably give Facilities Managers and Structural Engineering contractors nightmares for weeks.

TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering
www.bluetechnik.com

BigInch (Petroleum)
20 Feb 09 7:53
The compressive strength of concrete is NOT the bearing strength.  A kazillion pound load would give the owners of the facilities heart burn right in the pocketbook.

latinoguy,

Large heavy equipment often (on offshore platforms) can be skid mounted on heavy WF beams to spread out the loads.  Another possible option.   

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

latinoguy (Mechanical) (OP)
20 Feb 09 10:53
Thanks much guys! BTW, the CT is computed tomography, being used more often in other industries rather than just medicine.

Your distinction between compressive stress and bearing strength seems critical. Also, a maximum deflection capability seems critical as well. I understand that bearing plates, skids and other means can always be used to distribute equipment loads to bring them into more reasonable limits, but I'm still left with determining a practical upper load limit for equipment.

It sounds like I should approach this from the facility side, and take a reasonable guess on what the facility limits would be. Yet some of the equipment is quoted as being as high as 500 psf. Is this a reasonable limit for concrete slabs typically found in "light" industrial facilities? I've surveyed a few raised floor providers too, and even they have products with max "uniform" load of 650 psf (over 2ft x 2ft), and 2500 lbs max "concentrated" load (over 1 square inch) that yields a max deflection of .040 inches. Is there a good reference that suggests typical maximum values found in facilities such as warehouses and laboratories?
Thanks again!
BigInch (Petroleum)
20 Feb 09 11:30
I Googled CT and thought it might be the medical stuff, but you said industrial, so that didn't seem to fit.  

Most "light" buildings would be designed for a live load of only about 100 to 150 psf.  150 is getting relatively heavy (and costly) for light construction.

Industrial buildings might be in the range of 100 to 200 psf in storage areas.  I would class 500 psf as quite a heavy loading.

I'm curious.  Can you post a general arrangement dwg and a load footprint for these things?  (I was a structural engineer in a past life.)  

 

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

Helpful Member!  IRstuff (Aerospace)
20 Feb 09 14:55
I would think that the raised flooring might be AROUND the CT, but not under.  Many imaging systems require vibration isolation and sit on concrete blocks to minimize angular vibrations.

TTFN

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BigInch (Petroleum)
20 Feb 09 17:20
In that case, ground floor (or less) would seem to be an advantage in minimizing vibration.

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

latinoguy (Mechanical) (OP)
22 Feb 09 9:58
Thanks for all your replies. I wish I had an installation drawing - most manufacturers seem to want to do installation themselves, and each is different. In fact, you're right about stability and isolation for imaging systems, so I should assume a concrete slab for all installations. In any case, I did find a useful guide for facility loads at www.wbdg.org:

http://www.wbdg.org/ccb/DOD/UFC/ufc_3_310_01.pdf

As you suggested, this also recommends (based on IBC 2006) a MINIMUM uniformly distributed live load of 125 psf for general "light" storage warehouses. A MINIMUM concentrated live load of 2000 lbs is recommended for "light" manufacturing. I suppose I could use the higher of the minimums for "heavy" loads (i.e. 250 psf and 3000 lbs), but I still wonder if this is relevant for determining design limits on equipment, since all this depends on a particular building? Do you think the following equipment design requirement below is adequate?

"The imaging system shall have provisions for allowing installation within manufacturing, warehouse or other light industrial facility with a maximum uniformly distributed live load rating of 250 psf, and a maximum concentrated live load rating of 3,000 lbs.  Bearing plates, skids, framing or other means may be used to achieve this load rating, but must then be considered part of imaging system configuration."
BigInch (Petroleum)
22 Feb 09 12:12
The structural engineers tend to use those IBC loads as minimums AND maximums, unless they know in advance that specific equipment will be located inside and are looking the equipment load diagram, something that doesn't happen unless the building is being newly designed specifically for purpose in a chemical or industrial plant, etc.  Otherwise expect only to find around existing designs for around 150 psf absolute maximum.

I think your best bet is to spec a continuous railed skid, 4 ft between rails and no bearing plates (load concentrations), remembering that roughly 5/8 of a center point load will effectively bear down on the central 1/9th area (like on a 3x3 matrix) of any "uniform thickness plate-type" design.


 

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

larrylcoyle (Automotive)
23 Mar 09 18:30
latinoguy,

I purchased a high-speed CNC machine sever years ago and I was in the process of having my shop built at the same time.  I contacted the CNC manufacturer about the shop floor requirements and not only did they reply with drawings but they also provided me with the requirements of the concrete.  They gave me the psi rating and either the formula or the actual thickness for the concrete flooring immediately under the CNC machine.  They also provided a special mounting procedure to keep the machine from moving under any vibrations due to load or rpm or combination.

So, I would suggest contacting the manufacturer of your CT for their requirements and recommendations.  They will probably even furnish a project engineer to ensure this is done properly.

Larry

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