Loading on 2nd Floor Concrete Floor
Loading on 2nd Floor Concrete Floor
(OP)
Hello Structural Guru's,
I'm a mechanical engineering and develop automation equipment. I have a situation where our customer has provided a 5 kPa (104 psf) maximum 2nd Floor loading.
The floor thickness is 6" and it is reinforced with rebar. I don't know the details of the reinforcement or the span lengths. Our automation equipment will rest on the 2nd floor at points within the total footprint. The total foot print of the machine is 18.5 m^2 (199.5 ft^2). There are about 30 points loads of varying intensity within the footprint. The maximum point load pressure on one of the equipment footings is 14.00 kPa (292.4 psf). Obviously, this will not pass the 5.0 kPa (104 psf) requirement.
My question is can you assume that the equipment weight is distributed over the total footprint (resulting in a passing design) or must you determine the safety of the loading looking at each point load (resulting in a failed design)?
My gut says the design is okay...based on the simple fact that my shoe is 4" x 12" and I weight 193lbs. Therefore, I would place a 13.84 kPa (289.5 psf). If my gut is wrong my wife and I better not dance on that floor....ever!!!
Thanks in advance for you thoughts and assistance.
dmech
I'm a mechanical engineering and develop automation equipment. I have a situation where our customer has provided a 5 kPa (104 psf) maximum 2nd Floor loading.
The floor thickness is 6" and it is reinforced with rebar. I don't know the details of the reinforcement or the span lengths. Our automation equipment will rest on the 2nd floor at points within the total footprint. The total foot print of the machine is 18.5 m^2 (199.5 ft^2). There are about 30 points loads of varying intensity within the footprint. The maximum point load pressure on one of the equipment footings is 14.00 kPa (292.4 psf). Obviously, this will not pass the 5.0 kPa (104 psf) requirement.
My question is can you assume that the equipment weight is distributed over the total footprint (resulting in a passing design) or must you determine the safety of the loading looking at each point load (resulting in a failed design)?
My gut says the design is okay...based on the simple fact that my shoe is 4" x 12" and I weight 193lbs. Therefore, I would place a 13.84 kPa (289.5 psf). If my gut is wrong my wife and I better not dance on that floor....ever!!!
Thanks in advance for you thoughts and assistance.
dmech






RE: Loading on 2nd Floor Concrete Floor
RE: Loading on 2nd Floor Concrete Floor
RE: Loading on 2nd Floor Concrete Floor
Anyhow, when going outside my expertise I continually find that "keywords" are a great starting point to learning a subject and thereby further my knowledge. So, thank you both for "punching shear", "two-way shear", and "flexural capacity".
RE: Loading on 2nd Floor Concrete Floor
RE: Loading on 2nd Floor Concrete Floor
An example of a one way slab is as follows: say the equipment is 4' wide x 10' long, with the 10' dimension parallel to the intermitent beams, and the total weight is 5,000#. The spacing between beams where the unit is placed is 10' o.c. Further say 40% of the total weight is concentrated in the first 3' of one end. Therefore, worst case, this would result in 0.4 x 5,000#/3' = 667# per foot of slab width. For both shear and bending, if the unit load is is no more than one-half of what the psf load would be, then it doesn't matter if the load is immediately adjacent to a beam, or anywhere in between. Punching is a different matter, but it will not normally control unless you have a very large load on a very small footprint.
In your case, 104 psf x 10' span/2 = 520# per foot of slab width. Therefore, one-half of the psf load is less than the worst actual load placed (pounds per foot of slab width), so it apparently doesn't work. Only a more detailed analysis will give you the real answer. However, the procedure I describe will always be conservative for an otherwise unloaded area. If the 4' width of the unit straddles a beam, then you can look at each slab span individually. If it straddles, and if the unit weight is basically balanced side-to-side, you would only have 333# per foot of slab width, and it would work.