Rebar within development length

[windrunner888]

I encounter an approach that I am not quite familiar with. I use arbitrary number in the description below:

A 15’ long concrete drilled pier was reinforced using 10’ long post-installed rebars. The additional rebars have 4’ development length.

Resistance A: original rebar + post-installed rebar
Resistance B: original rebar

From top to bottom, the engineer used:
0-6’: Resistance A
6’-10’: Resistance A at 6’, linearly reduced to resistance B at 10’
10’-15’: Resistance B

I am wondering if using partial resistance of rebar (6’-10’) is justified? I usually don’t consider contribution of rebar within its own development length (hard cut-off, I would use resistance B from 6’ to bottom). Any codes that allowing (or disallowing) it?

Thank you!

 

[Lomarandil]

With some exceptions (cases needing ductility, shear friction, etc), ACI has allowes the required development length to be reduced by the proportion of steel required versus steel provided.

This is widely interpreted to indicate a linear gradient of available bar area/capacity from zero at the undeveloped end to full capacity at the development length (for straight bars).

As such, the approach this engineer has taken doesn't surprise me, and would generally be considered reasonable, although I'm not sure whether it is explicitly backed in the code or commentary.

----
just call me Lo.

 

[KootK]

I agree with Lomarandil. Similarly, concrete texts and software will usually show beam flexural capacity climbing linearly over the development length of additional bars as those bars are introduced. This concept is also baked into the provisions for the anchorage of positive flexural reinforcing.