Slab on ground to ACI codes

[Karlos80]

Hi All,

I am designing a large slab on ground to the ACI standards, however I have only experience in designing to the EN codes and TR34. When using the ACI approach (unreinforced slab) I am getting a very thick section in comparison to TR34. The reason is that the ACI only allows to design unreinforced slab and TR34 reinforced (bottom mesh). For example using the PCA charts for two racking legs (back to back, 300mm apart) with a load 25000psi (total load for two legs), over 24inch2 total contact area and 96x44inch racking spacing I am getting 10.7inch slab! This is considering FOS 1.7. Not to mention when design the load on the edge of the slab!

For the TR34 approach I am getting 175mm slab with A193 mesh bottom which is ok. But unforunetly I need to comply with the ACI

Any toughs please? Maybe I am getting this all wrong?

Regards
Karol

 

[Karlos80]

All,

Anybody can help me in relation to the above please???

Karol

 

[fegenbush]

What is your reference for thinking that an ACI 318 slab does not allow reinforcement? I read 7.12.2.1 as requiring 0.0018*Ag minimum reinforcement for temperature and shrinkage effects. If the members are in bending, there is a minimum reinforcement for that as well.

 

[hokie66]

fegenbush,
ACI318 does not apply to slabs on ground. There is another ACI reference which does, and I think the OP will get some comment on that, probably after the weekend.

 

[Karlos80]

fegenbush ,
I am using ACI 360R-10 "Guide to Design of Slabs-on-Ground".

 

[Once20036]

"The reason is that the ACI only allows to design unreinforced slab..."

ACI 360-06 pg 30 indicates that when flexural tensile stress exceeds the allowable, you can increase the thickness or provide reinforcement to provide all of the tension indicated by the analysis.

 

[Karlos80]

I wonder if anybody can double check if my understanding of the ACI360 standards is correct :

I got a 10.6 inch slab (270mm) based on the following assumptions : safety factor 1.7, concrete strength fc =4500psi (40N concrete), subgrade k=200 pci (10% CBR), Concentrated load P = 25000 lbs (approx 120kN – double racking leg concentration), contact area 23.20in2 (30000mm2 – two baseplate assuming 150x100mm each).

The 270mm slab on ground sounds very thick to me for the loading provided. Thus not sure if I am using the ACI standards correctly?

Regards

 

[Karlos80]

Lads,
Really need help on this!

 

[MrHershey]

Check out 'Designing Floor Slabs on Grade'. Lots of great information and walkthroughs for designing slab on grade for wheel loads, post loads, etc.

link at amazon.com