Expert: Arshad Khan - 3/10/2001

Question
Hello Mr. Khan,

Good Day,
I have two questions for you in the above mentioned subject.
We have an industrial facility floor(Suspended Floor- Not slab on grade). This floor will be constructed with Reinforced Concrete materials.
Our UDL is 250 psf(1.23T/M2)in addition to forklifts(we do not know how many will be utilized in the facility!)the max capacity of the forklift shall be limited however to 6 Tons.
My first question to you is:
If we do not want to analyze the floor for the wheel(concentrated load) of the fork lift and only work with UDL(except of cource for punching)
What do you think a good UDL would be adequate to cover both,the 250psf & the 6-Ton forklift?(say each front wheel load is 3Tons)
Please note that the forklift can be anywhere. Further, the framing plan is not yet established.
It can be two-way or one-way edge supported solid slabs where the module(max.column spacing in any one direction is limited to 6m)or one-way ribbed slab!(note:for both questions,assume one-way behavior of slab for the effect of point load)
The second question is:
Assuming you have a square or rectangular solid slab(say 7x6m panel)and you want to design this simply supported panel for the 6-Ton forklift mentioned above(again we do not know at this stage how many will be used)and the forklift can be anywhrere.
a.For this panel(7x6)and if the dimensions of the forklift are(1.2width x 2.5length in meters) and the wheel spacing is 1 meter. How would you simulate or how many forklifts would you design the panel for?(e.g.distances between adjacent forklifts in all directions and as a result what is the design concentrated loads&can you convert this into an equivalent UDL?)

b.For one-way shear capacity of this slab(Not two-way punching shear), what is the effective width on which the shear is supported(@the edge and away from the edge.The Edge is a supporting beam)?

Answer
Hi Mr. Jarkas,

You have asked several questions, all of which are inter-related. If I have my units correct, then you have a UDL design load of 12 kN/m2, PLUS a forklift of 60 kN (including self weight?).

Now, the answer is simple. If the forklift has a footprint of 1.2m X 2.5m, I would assume that any 2 or 3 forklifts would not come closer to eachother than say 1.0m. The effective footprint for load purposes can therefore be assumed at 2.2m by 3.5m, which gives 7.7m2. Divide 60 kN by this and you have 8 kN/m2.

Now, you physically cannot have the same area of slab loaded by 12 kN/m2 (250 p.s.f) and the forklift at the same time. So, I would design the whole slab for 12 kN/m2, or if you wish to be conservative, 15 kN/m2., but do check for punching shear as you have noted.

Finally, the shear transfer to a supporting beam can be taken as a 60 degree spread from each wheel, taking into account the overlapping of adjacent wheels or forklifts. This assumes that the slab is solid. If it is ribbed, then it gets more complicated as this depends on the relative stiffness of the flange when compared with the rib, and also the rib centres. If ribs are no more than 0.6m apart and the flange is at least 125 to 150 mm thickness, then you can assume that the load/shear is shared between at least two adjacent ribs.

However, you should also check for the case when a wheel is directly on top of a rib, close to a supporting beam - in that case 100% of the load is carried by the single rib.

I trust this answers all your questions.
Kind regards,

Arshad