Pullout Strength of Tension Rebar
Pullout Strength of Tension Rebar
(OP)
Do you know how to calculate pullout strength of single tension bar usually used in pile caps. Enough distance from edges no worries about side face blowout. Some books say to use Un = 35*SQRT(Fc'). Based on ACI 318-14 Equation 25.4.2.3a, Ld would be quite large (ld=71*db) seems impractical. Pile cap thickness is 30 inch in my design. Will appreciate your response.






RE: Pullout Strength of Tension Rebar
First, make sure you are using the shortest ld allowed by Code. In ACI 318-11, there are two different formulas, and you are free to use either one.
This value of ld is what is required to develop the full yield strength of the bar. If your development length is less, you can calculate the capacity of the bar by multiplying the full yield strength by (development length available/ld). Note that this is only permitted when you need not develop the full yield strength.
Your other option is to hook the bar--development length of a hook will be much less.
DaveAtkins
RE: Pullout Strength of Tension Rebar
RE: Pullout Strength of Tension Rebar
1) Development of the bar ensures that the rebar won't pull out from the concrete due to a bond failure.
2) Development of the bar does NOT ensure that a concrete breakout failure will not occur.
As such, I would do one of two things:
1) Effectively lap the rebar with the rebar in the elements above and below.
2) Use Appendix D provisions for post installed rebar to assess pullout capacity.
My opinion on this tends to be controversial so digest it with that in mind.
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.
RE: Pullout Strength of Tension Rebar
For a reinforcing bar embedded in a mass of concrete, I think Chapter 12 (the development length chapter) of ACI 318-11 applies. Appendix D does not apply.
Using KootK's thinking, all reinforcing bars, in all situations, would need to be checked using Appendix D.
DaveAtkins
RE: Pullout Strength of Tension Rebar
There is no room for overlap from anywhere. Only where there are anchor bolts it may be possible. Usually practice is to leave it alone and try to satisfy any column tension. Question is how do I ensure the provided embedment length is good enough to take the axial tension. Assume that no bending/flexure involved.
Using (ld/db) = (3/40) * (fy/sqrt(fc') * (alpha*beta*gama) / ((c+Kct)/db)
and assuming Kct = 0 as there is only one bar going into the pile cap
getting ld = 23.72 inch (fy=60000,fc'=4000, db=1 in, alpha=beta=gama =1
Do you think is good
RE: Pullout Strength of Tension Rebar
Not so. The vast majority of the time we are dealing with reinforced concrete principles whereby rebar tension is restrained by concrete struts/compression fields. It is only in cases such as the one being discussed here, where there is no concrete strut available to restrain the rebar, where we are forced to resort to using concrete tension (app D etc) to restrain rebar tension.
I argued my case for this concept extensively here: Link.
If you post a detail showing your condition and the forces that you're looking to transfer, we'll be happy to review it.
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.
RE: Pullout Strength of Tension Rebar
RE: Pullout Strength of Tension Rebar
use 0.9 X fy X Abar to calculate the design tension strength.
RE: Pullout Strength of Tension Rebar
RE: Pullout Strength of Tension Rebar
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.
RE: Pullout Strength of Tension Rebar