jropert
Structural
- May 18, 2010
- 23
I'm tasked with checking an existing 5" thick fiber reinforced concrete "housekeeping" pad for new equipment loads. This is a very large existing pad (approximately 1300SF) that will support multiple new pieces of equipment (some permanently anchored to the pad and some movable on wheels). This pad sits on the building's slab-on-grade which must be at least 6" thick (not confirmed, but based on the heavy industrial use of this slab, it appears that this would be reasonable). We had a testing agency perform cores thru the equipment pad and obtained an average compressive strength of 3,000psi.
I have two loading conditions I'm not sure how to go about confirming acceptance on the existing pad.
(1) A large machine (25,000#) supported on two full length rails (one each side of machine).
(2) A small 4,000# movable machine on 4 solid caster wheels.
All other pieces of equipment a lighter and are supported on stands/feet that appear to be sufficient (i.e. checking bearing strength per ACI 318 Ch. 10).
My approach for checking (1) is to use the GRDSLAB.xls (found from a previous thread) which utilizes the allowable uniform load method of the Army TM 5-809-12 manual ("Concrete Floor Slabs on Grade Subjected to Heavy Loads") and PCA "Slab Thickness Design for Industrial Concrete Floors on Grade". This appears to be a close representative of this machine condition as there would be an "aisle width" between the rails with uniform loading on either side along the rails. Would this be a correct approach? If so, would it be safe to assume a high subgrade modulus (say 400pci which is the max the spreadsheet will go) as the "subgrade" under the pad in question is actually a concrete slab?
I'm not sure how to check (2) since the casters have a very small contact area (using "Contact Mechanics" by Burns & McDonnell) which would not allow me to use the PCA charts for single axle checks. Is there a way to check this machine? I can't imagine that a 4,000# machine on casters would "not work" on this 5" pad and would require "armoring". There is fiber reinforcement which will help mitigate cracking, but again, is there another type of design check?
I don't have the ACI 360 or the PCA slab design books, but only ACI 318. Is it necessary to obtain the ACI 360 to check for the above conditions?
Any help or advice would be greatly appreciated.
I have two loading conditions I'm not sure how to go about confirming acceptance on the existing pad.
(1) A large machine (25,000#) supported on two full length rails (one each side of machine).
(2) A small 4,000# movable machine on 4 solid caster wheels.
All other pieces of equipment a lighter and are supported on stands/feet that appear to be sufficient (i.e. checking bearing strength per ACI 318 Ch. 10).
My approach for checking (1) is to use the GRDSLAB.xls (found from a previous thread) which utilizes the allowable uniform load method of the Army TM 5-809-12 manual ("Concrete Floor Slabs on Grade Subjected to Heavy Loads") and PCA "Slab Thickness Design for Industrial Concrete Floors on Grade". This appears to be a close representative of this machine condition as there would be an "aisle width" between the rails with uniform loading on either side along the rails. Would this be a correct approach? If so, would it be safe to assume a high subgrade modulus (say 400pci which is the max the spreadsheet will go) as the "subgrade" under the pad in question is actually a concrete slab?
I'm not sure how to check (2) since the casters have a very small contact area (using "Contact Mechanics" by Burns & McDonnell) which would not allow me to use the PCA charts for single axle checks. Is there a way to check this machine? I can't imagine that a 4,000# machine on casters would "not work" on this 5" pad and would require "armoring". There is fiber reinforcement which will help mitigate cracking, but again, is there another type of design check?
I don't have the ACI 360 or the PCA slab design books, but only ACI 318. Is it necessary to obtain the ACI 360 to check for the above conditions?
Any help or advice would be greatly appreciated.
