punching shear capacity of piled slabs
punching shear capacity of piled slabs
(OP)
checking punching shear of piles, does anyone use the two layers of steel as the area of rebar? I have always used the one layer (in tension zone). seems to be a bit of disagreement in speaking to people on whether 2 layers can be used. i.e. have same rc in top and bottom of slab continuing over pile head.






RE: punching shear capacity of piled slabs
RE: punching shear capacity of piled slabs
It seems to me that the steel is there and would have to fail if the concrete were to fail.
RE: punching shear capacity of piled slabs
RE: punching shear capacity of piled slabs
Research is always done on the type of applications for which a concept is intended. Extrapolating research to applications not expected is not appropriate, in my opinion.
If ACI intended the Shear Friction concept to be applied to beams and slabs, then I don't think they would have carefully worded the applications in 11.7.1. They would have simply said that it applies everywhere.
RE: punching shear capacity of piled slabs
Dont use the bottom reinforcement.
RE: punching shear capacity of piled slabs
RE: punching shear capacity of piled slabs
I'll check the CIRIA flat slabs design guide when I get to work tomorow.
RE: punching shear capacity of piled slabs
I agree with miecz. You cannot extrapolate shear friction to this method. Shear friction assumes the surface is cracked or is going to be cracked and shear friction alone resists the forces. I believe I would not like to rely on shear friction to resist foundation loads. The design methodology for shear in concrete for punching shear assumes the concrete resists the shear alone. There is no help from reinforcement. You can reinforce for punching shear in slabs using some kind of shear head reinforcement as per the ACI 318-05 code. There is an example in PCA Notes on ACI 318. I don't see why you would want to use shear heads to reinforce for punching shear. Just make your cap thicker. We never use reinforcment for punching shear in footing of any kinds and I do commercial and industrial work.
RE: punching shear capacity of piled slabs
RE: punching shear capacity of piled slabs
RE: punching shear capacity of piled slabs
RE: punching shear capacity of piled slabs
RE: punching shear capacity of piled slabs
RE: punching shear capacity of piled slabs
RE: punching shear capacity of piled slabs
RE: punching shear capacity of piled slabs
RE: punching shear capacity of piled slabs
RE: punching shear capacity of piled slabs
Clause 3.4.5.4 references Table 3.8 and clearly states that As is the area of longitudinal tension reinforcement which is adequately anchored.
Bottom 'compression' steel can only be used in a specific case where the beam has been designed as simply supported but is cast monolithically with the column.
I can't see justification anywhere for combining the top and bottom steel.
Shear cracking initially develops at or near the tension steel and it is the cross-section area of this steel which directly affects when cracking will start.
RE: punching shear capacity of piled slabs
Logically the top and bottom rebar must fail for punching to occur this suggests that from an engineering point of view there is justification to use the full area of available steel. One way to look at is to check whether the bottom steel adjacent to the pile is required in your design for flexure and whether it can be defined as compression rebar.
There is a handbook to BS8110 which describes this in detail, but unfortunately I don't have all the details of the publication with me now.
RE: punching shear capacity of piled slabs
RE: punching shear capacity of piled slabs