Headed Bars v/s standard reinforcement codal requirements per ACI 318-19

[nampar]

Hi All,
I have a question that involves substitution of standard reinforcement with headed bars for a beam.

Please refer to the attachment for code section (ACI 318-19).
• For beams with regular reinforcing; we generally use 25.2.1 for rebar spacing and clear cover of 1.5” if it is an interior beam.
• Now in my case, we are using #11 rebars. So if I follow 25.4.4.1, my rebar c/c spacing becomes 3*1.41=4.23” and clear cover becomes 2*1.41=2.82” (significantly higher than what I would use for reinforcement without heads)

In order to approve this substitution, I believe we need to check the design and provide updated clear covers and rebar c/c spacings per 25.4.4.1. Is my understanding correct? (or can we use the same design clearances as we did for reinforcing without heads? Is there a valid justification for this?)

Thank you in advance for your insights.

 

[KootK]

Is my understanding correct?

Yes, I would say so.

...or can we use the same design clearances as we did for reinforcing without heads? Is there a valid justification for this?

Not that I can think of. If 318 has specifically asked for greater cover and spacing for headed bars, it seems reasonable to me to assume that they did so for a legitimate reason. I can't say for certain what that reason is but, were I to speculate, I would guess:

1) Making sure that the heads don't physically overlap or project outside of the concrete.

2) Making sure that the high local stresses behind the heads don't produce local concrete splitting there.

This will be an imperfect analogy but you can kind of consider a bar head mechanically equivalent to a hook in some ways. And, in this instance, it's a bit like if the hook were faced the wrong way.