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why does confining reinforcement increase development length?

why does confining reinforcement increase development length?

why does confining reinforcement increase development length?

(OP)
my goal is to use (cb + Ktr)/db value of 2.5 to reduce development length. this "without confining reinforcement" is confusing me. I'm developing anchor bolt embedment to pedestal reinforcement. are pedestal reinforcement ties considered "confining reinforcement"?

taken from aci 12.2.3 commentary.

"For example, bars or wires with minimum clear cover not less than 2db and minimum clear spacing not less than 4db and without any confining reinforcement would have a (cb + Ktr)/db value of 2.5 and would require a
development length of only 28db for the example above."

RE: why does confining reinforcement increase development length?

cb = 2*db cover (or 1/2 of 4*db spacing) + 0.5*db to center of bar = 2.5*db
Ktr = 0 (no confining reinforcement)
(cb+Ktr)/db = 2.5

I guess I do not understand your question.

DaveAtkins

RE: why does confining reinforcement increase development length?

(OP)
@dave, even with confining reinforcement, I can still have (cb+Ktr)/db = 2.5?
sorry, I didn't try to compute the formula. i just used either 1.5 or 2.5 as (cb+Ktr)/db.

RE: why does confining reinforcement increase development length?

As I understand it:

-All reinforcement produces bonding stresses in the concrete in the area around the bar, generally acting normal to the angled face of the deformations.

-Embedment depth is directly proportional to the bonding stresses required at yield capacity of the steel in question.

-As you have two elements producing bonding stresses possibly in the same area, the code chooses to require a larger bonding area for one member to compensate. This will reduce possible cracking between the two bars where the failure cylinder overlaps.

-There are ways to calculate the bonding stress for each bar given its development length, you should be able to run these numbers for your stirrups and anchors, and then specify your development length & minimum clearance between the two elements.

Note - I'm still learning this so someone with more experience might want to confirm and/or correct.

RE: why does confining reinforcement increase development length?

(OP)
got it. I should have looked at PCA notes examples. ACI commentary wasn't clear for me. thanks,

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