Anchor rod length greater than 25''

[BAGW]

Hi,

As per ACI318-11 and IBC-2012, Equation D-6 of section D 5.2 can be used to calculate the anchor bolt tension capacity for concrete break out right? This is how I am interpreting ACI and IBC. Am I correct?

 

[BAGW]

Sorry for incomplete query. I would like to know if equation D-6 of section D 5.2 (breakout of anchor) holds good for anchor bolt length greater than 25'' in length.

 

[JStephen]

In the commentary in ACI 318-05, I think they say that limitation (and/or the bolt size limitation) was based on the limits of testing that had been done.
I've assumed that additional depth increases, rather than decreases, breakout, and in most cases, my bolts will work by assuming 25" length even if actual length is longer.

 

[BAGW]

@JStephen,

Are you tending to say that increasing the embedment depth, the breakout increases or am I reading it wrong? If we have enough edge distance, increasing the embedment depth, the concrete breakout capacity for the anchor bolts goes up and hence decreases the breakout action. Reading through ACI-11 and IBC-12, they state that "The concrete breakout strength for anchors shall be considered satisfied by design procedure of D.5.2 provided Equation D-7 is not used for anchor embedments exceeding 25 inches". As per this, Eq D-6 of section D 5.2 hold good for anchor bolt having embedment depth greater than 25''.

 

[JStephen]

I'm assuming that if actual depth exceeds 25", then using 25" in the calculations instead of the actual depth is conservative.

 

[KootK]

I don't disagree with anything above but, beyond 25", I'll start thinking of things in terms of reinforced concrete (passing loads from anchors to rebar) rather than appendix D, unreinforced / nominally reinforced concrete anchorage.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.