PCA Method for designing industrial concrete slabs on grade 1

[NFrancis]

I'm designing a concrete slab that going to see an axle load of around 137 kips. My concern is with the contraction joints. PCA method mentions every 18', I doubt that the cost estimate for the foundation accounted for all the dowels/support baskets that would be necessary to follow these guide lines. Any suggestions? Slab is 72 m x 36 m, 18" thick (T and B layer of temp and shrinkage steel) w/ thickened edges. Thanks

 

[Ron]

Your loads are way too high to consider having joints without mechanical load transfer. Dowels are necessary.

The joints are necessary as well. For that thickness of slab, you can stretch your joints out a bit more than 18 feet, but 20 feet is fairly common for airfield slabs, which often have similar thickness.

In your case a 6m joint spacing,each direction, would work well. Require that the joints be cut to a depth of at least 100mm within 8 hours of placement.

 

[NFrancis]

So rather than just laying the bars continuous we have to place "18' x 18' groups" of bars with perimeter dowels/baskets? Why do the dowels need sized for shear transfer when the method assumes the load transfers directly to the subgrade? What have you seen happen (or heard) if dowels are not used?

 

[Ron]

The joint load transfer is done to prevent a discontinuity in the load distribution...one side of the joint is loaded, the other is not...promotes pumping and slab cracking from the sudden load gain/loss across the joint. Dowels help to mitigate this condition, tranferring the load across the joint from one slab to the other.

The dowels are usually placed at about 12 to 18 inch centers, placed at mid-depth and are continuous for the length of the joint in the transverse direction. Tie bars are used along the outside joints to keep the slabs from drifting outward. Longitudinal dowels may be required if your traffic pattern is non-uniform and crosses other joints equally. In that case, be sure to leave the dowels out near the joint intersections.

 

[Qshake]

Good one Ron.

What about grease on the end of the dowel, is that also recommended/required? for temperature and shrinkage allowance.

Regards,
Qshake

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[rowingengineer]

also if you can transfer the load across the joint (say 80%) then normally this will allow you to adopted the internal design thickness. I don't know your design reference and geo conditions but at the load and thickness you are talking i would assume you have designed for edge loaded conditions. Have you considered PT or Reinforced design?

Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it

 

[NFrancis]

Well... Enough said, thanks for the advise, I appreceate it.