Rebar Development Length vs Anchors 3

[Logan82]

Hi,

Is it possible to use ACI 318 Rebar Development Length formulas to design post installed anchors (rebars) that are in tension only?

Also, if I understand correctly, Rebar Development Length formulas are for rebars in tension only, whereas post installed anchors formulas are for tension + shear.

 

[hetgen]

Check this thread

 

[Logan82]

Hi,

I have read the thread you have linked. While it is very interesting, and it brought me more questions to ask, it does not specifically answer my question.

 

[BridgeSmith]

In a word - No. For most, maybe all, adhesive anchorage systems for post-installed anchor bars, using the development length provisions would be conservative for development of the bars (transferring the force equal to the yield capacity of the bar to the concrete through mechanical interlock and bond). However, required anchorage (adequate embedment to prevent a 'cone' failure of the surrounding concrete) is another matter. That is typically determined (and tabulated in tables) by the adhesive anchorage system manufacturer. All the adhesive anchor manufacturers that I have seen, have tables of required embedment depth for rebar as anchors.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[Logan82]

Thank you for your answer BridgeSmith. I think you are right regarding the fact that development length can be used for existing concrete. I have just found a calculator for Simpson Strongtie that calculates exactly that:

Source:

https://www2.strongtie.com/webapps/rebardevelopmentlengthcalculator/

To follow on your comment, and on the thread that was linked by hetgen, here are some reasons that may indicate that the development length theory considers concrete cone breakout (however I am not sure about this and Inputs on this subject would be greatly appreciated):

- In the development length formula (ACI 318-19 25.4), the rebar spacing and the distance from the edge are taken into account. I would have thought that some form of failure other than pullout failure mechanism would have been taken into account due to these factors.

- If the development length requires reinforcement in the concrete to which it is attached, what is the use of the concept of rebar lap splice length (ACI 318-19 25.5)?

- On this video on development length by professor Tyler Ley,

https://www.youtube.com/watch?v=WXtULdXMCfo,

the video starts with what appears to be a concrete cone breakout failure at 1:48

 

[canwesteng]

If you use adhesive to develop the bar in tension, then where does the tension from the rebar go?

 

[KootK]

In the development length formula (ACI 318-19 25.4), the rebar spacing and the distance from the edge are taken into account. I would have thought that some form of failure other than pullout failure mechanism would have been taken into account due to these factors.

Humor me and consider some KootK originated definitions which reflect the truth as I know it to be:

1) Development = what it takes to prevent a bar from ripping from the concrete with little to no concrete attached to it. Basically bond stress in the parlance of an earlier time.

2) Anchorage = what it takes to prevent a bar from ripping from the concrete... period. This requires one of the following:

a) Adequate development AND a compression strut for the rebar to push against that prevents breakout. Many would consider this just reinforced concrete design rather than true anchorage.

b) Adequate lap splicing (a permutation of development) to another piece of reinforcement. Many would consider this just reinforced concrete design rather than true anchorage.

c) Adequate development AND the absence of concrete failure frustums that breakout before the requisite load carrying capacity is reached. This is effectively what many of us were first introduced to as the loathsome ACI Appendix D. Prior to that, it was Nelson Stud design guides etc.

3) Note that development does not require anchorage but anchorage DOES require development.

4) ACI considers spacing and edge distances in the development length equations to design against concrete splitting. In a sense, sure, that probably does represent a concrete breakout mode after a fashion. However, that's only ONE possible breakout mode and anchorage has not been achieved via #2c until the rest are checked as well.

5) The tests done to determine development were set up such that they did in fact provide concrete struts for the tensed rebar to react against. That's #2a above and precludes the concrete breakout failure modes that most of us now associate with "anchorage".

 

[Logan82]

If you use adhesive to develop the bar in tension, then where does the tension from the rebar go?

If there is no concrete failure around this rebar, then the concrete mass should receive the tension from what I see. What I was wondering is if development length (ACI 318-19 25.4) verifies the same concrete anchor failures as ACI 318-19 17).

Interesting KootK!

However, if development length does not verify all concrete breakout failures, in which context can you use development length without a lap splice configuration?

If we consider development length calculation in new concrete, do we have to also calculate it as an anchor to have all concrete failure cases?

(Example I found on the Web)

 

[KootK]

However, if development length does not verify all concrete breakout failures, in which context can you use development length without a lap splice configuration?

#2a & #2c in my previous post.

If we consider development length calculation in new concrete, do we have to also calculate it as an anchor to have all concrete failure cases?

Nope, that's a case #2a per the sketch below.

 

[Logan82]

Your answer makes it clear, thank you!

 

[KootK]

You're most welcome Logan82.