Minimum Reinforcement Splice Lengths for Ground Slabs 2

[ZiadSem]

What is the minimum overlap/splice length for reinforcement in a slab-on-grade? Assume we have a 200mm thick ground slab reinforced with 12mm @ 200 c.c both ways. The ground slab is for a storage facility with moving forklifts. The main concern here is that ground slabs do not usually experience pure flexure as in the case of suspended slabs, and the main function of reinforcement is to resist shrinkage & temperature stresses (more or less), therefore does the minimum splice length decrease compared to the regular tension splice?

 

[KootK]

Temperature and shrinkage steel needs to be developed for Fy. If you're using the slab on grade for that purpose, I'd recommend full tension laps.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[asixth]

I too would recommend using the full lapped splice length.

By the sounds of it you have a moderate-high level of crack control steel in there. If you used a reduced lap length then you would be creating a zone of lesser crack control.

 

[ZiadSem]

Thank you for your feedback. I would also agree that there is a high level of crack control steel (I didn't mention that there is two layers of steel with the mentioned configuration. In my opinion, with such amount of steel, the concrete slab will never experience stresses that will yield the reinforcement). In my case, it is important to calculate the minimum acceptable splice length because we have a large area or concrete flooring (approx. 8,500 m2), and any unnecessary overlap will result in significant waste of steel reinforcement.
On the matter, ACI 318-08 Section 12.15.1 states that the minimum tension lap splice shall not be less than 300mm (even if the calculate development length is less), can any of you justify this requirement?

 

[KootK]

I imagine that the justification would be something like this:

1) A 300 lap on bars permitted to be 150 apart is barely a lap at all.
2) Who is going to balk at a 300 lap?

This really strikes me as the wrong way to go about saving money here. If you shave all of your laps down by half, you might reduce your steel weight by maybe 5%. You'd be better off justifying fewer bars and lapping those bars properly.



The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[JAE]

Section 7.12.2.3 of ACI 318-11 requires full fy development for Temp/Shrinkage steel (per KootK's statement above). Therefore, a Class B splice (1.3 x ld) is required.



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[ZiadSem]

Thank you for the feedback.