Structural Plain Concrete
Structural Plain Concrete
(OP)
I am checking a slab founded on rock loaded by steel strand anchors for two way shear (punching shear). Analysis shows #9 bars @ 12" in both directions are required to resist flexure. This does not meet the requirements of ACI Eqn. 10-3 for min reinforcement of flexural members but does satisfy ACI 10.5.3.
The question I have is should this slab be considered as Structural Plain Concrete since it does not have minimum reinforcement? By definition, plain concrete is structural concrete with no reinforcement or with less reinforcement than the minimum amount specified for reinforced concrete. I am unsure if by following ACI 10.5.3 does this then classify the slab as reinforced concrete?
The question I have is should this slab be considered as Structural Plain Concrete since it does not have minimum reinforcement? By definition, plain concrete is structural concrete with no reinforcement or with less reinforcement than the minimum amount specified for reinforced concrete. I am unsure if by following ACI 10.5.3 does this then classify the slab as reinforced concrete?






RE: Structural Plain Concrete
If #9's at 12 inch doesn't meet ACI 318, how thick is the slab? Back figuring, that comes out to about 2'-3". And the minimum of 10-3 can be exceeded if you have 1/3 more reinforcing than is required by analysis.
But to answer your question, since the slab is on rock, it shouldn't see bending. So the bending reinforcing minimum doesn't apply. I would call it reinforced concrete as long as it meets the temperature and shrinkage reinforcing limits.
RE: Structural Plain Concrete
Thank you for your response. I have attached a picture of the structure for clarification. I understand your question of punching shear when the slab is on rock, however, the forces (P) are very high, in the order of 1900 kips (unfactored). The thickness used for analysis is 4.5' and the remaining is used for cover. The situation to consider, as you pointed out, is will the slab "bend?" If not, then this question resolves itself.
RE: Structural Plain Concrete
Doing a rough calculatrion, the shear cone would have a perimeter of at least 9' x 9'. So 1900 kips divided into 81 square feet is 23 ksf, unfactored. What does your Geotechnical Report say about the rock capacity?
RE: Structural Plain Concrete
RE: Structural Plain Concrete
Dik
RE: Structural Plain Concrete
RE: Structural Plain Concrete
Deflection is a seperate issue. With that thick of slab, everything is going to deflect equally, so it's just whether you can live with some overall deflection.
RE: Structural Plain Concrete