Confilct between AS3600 and ACI318 (Punching reinforcement)

[Matt_Struc]

There seem to be a clear confident between the way AS3600 distribute the punching shear reinforcement and what ACI318 thing reinforcement should be spaced.

first AS3600 chapter 9 c.9.2.6 states that maximum spacing of punching shear reo ( ties) should not exceed 300 or Depth of slab.
ACI on the other hand R8.7.6d shows that stirrups spacing shall not exceed effective depth/2 half what AS3600 allows for.

one more thing, AS3600 c.9.2.6 states that the width of the stirrups should be as big as possible within a, a being the with of the critical punching shear area.
ACI however limits the width of the stirrups to 2d which might be much less than the previously mentioned a.

has anybody else came across this conflict and knows the logic behind both codes.

Thanks in advance, and looking forward to hear your responses.

 

[rapt]

If you read the commentaries to both codes you will discover the difference.

AS3600 currently only considers torsion reinforcement as increasing shear capacity.

 

[Matt_Struc]

Rapt, can you please elaborate. I have read both commentaries still can't seem to get an answer

 

[rapt]

C9.2.4 in the AS3600 commentary explains it much better than I can!

 

[Matt_Struc]

Dear Rapt, I am only discussing torsion reinforcement and how AS3600 and ACI specify different spacing for it. I have a basic understanding of the punching shear model.
The issue for me is, how come AS3600 specify spacing of ties to be max of D or 300 while ACI limits it to d/2.
same goes for the allowable width of the tie.

 

[rapt]

There is a fundamental difference in how the reinforcement is considered in AS3600 compared to ACI which you still do not seem to understand.

In ACI the reinforcement is basically contributing to a shear head and can be used to resist vertical shear without torsion (no moment transfer).

In AS3600, the reinforcement can only be used to increase the capacity due to torsion (moment transfer). There is no way in the AS3600 formulae to design shear reinforcement to resist vertical shear only.

The AS3600 model defines a torsion strip, and that controls the dimensions of the ties (width). Obviously the AS3600 committee at the time thought that a maximum spacing of 300 or D was sufficient for torsion reinforcement.

Eventually AS3600 will change to another punching shear model, but that will not happen until at least 2022 based on the current development schedule.