Expert: Arshad Khan - 3/29/2001

Question
Dear Mr. Khan,

Hello again and hope you're doing great.
This time I don't have a specific question, it's a general one but still in the area of Reinforced Concrete.
Now, let us assume the structural engineer receives the arch. drawings for an industrial facility and the owner or user still does not know how many and/or what forklift's capacity will be used in the factory, but the machines are known together with their weights and dimensions.
I have noticed several times that most structural engineers just work with the machines loads by dividing the total load of any one machine by its dimension and design the floor(Suspended slabs)for the largest load(UDL)without:
1. Checking the machine supporting details(they assume that the machine is resting over its dimensions(LxW)on the slab, despite the fact that most machines are supported by either legs or continuous channels or beams,and
2. Asking or even care if forklifts shall be used .
Is this OK on the one hand?!, and if you're faced with this(i.e. Doesn't know how many or the capacity of forklifts to be used) what would you do as far as the design of such suspended slabs on the other?
Furthermore, what is the best simulation criteria for forklifts on slabs panels(i.e. how many forklifts would you put on any one panel if your panel say e.g. 5x6 or 6x7...etc., and what spacings between them would you allow? assuming they could be anywhere on the factory floor.)
I'm mainly interested in this area as I'm working on establishing a criteria and design guidlines for the analysis and design of reinf. concrete industrial facilities, and your assistance and recommendations would be greatly appreciated.
Thank you and all the best.
Looking forward to hearing from you.
Sincerely,  

Answer
Hi Jarkas,

Your question is very difficult to answer as there are so many variables. Basically, whether one uses a UDL load for machines or works out exactly the load distribution depends on the relative sizes of the machines and floor panels, and also the likely locations of the skids, etc. If say the panel is 6m by 6m and it will have 4 machines, each of 2m by 2m footprint, then it is reasonable to take the total load as UDL. If on the same panel you have one machine of 2m X2m, which is very heavy and not sitting centrally, then it would be prudent to do a more detailed analysis.

Also, please do not forget to allow for dynamic loads from machinery and forklifts.

Regarding the forklift, one has to know from the client how many forklifts he intends to use, but in anycase it would be unreasonable to expect more than 2 forklifts to be operating in close proximity of eachother (so, assume the load of 2 forklifts, say 1m apart).

I have already given more guidelines to you as to how to distribute the wheel loads.

I hope this helps.

Kind regards,

Arshad Khan