ACI 318 Anchoring deformed bars

[Robin1020211]

Hello,

Is there anyone who could help me calculate the minimum required anchor length for one ribbed rebar using the ACI 318?

In Eurocode 2, you need to follow these steps to calculate the length:

lb,rqd = (φ / 4) (σsd / fbd) (required length)

fbd = 2.25 η1 η2 fctd (bond strength)

Then, under certain circumstances, you may apply a reduction:

lbd = α1 α2 α3 α4 α5 lb,rqd ≥ lb,min

In the ACI, I was referred to Chapter 17, however, I only find bolted anchors there?

Thanks in advance,

Robin

 

[BulbTheBuilder]

Refer chapter 25 of ACI - development length

 

[Robin1020211]

Thanks!

Is the development length independent of the force that acts on the anchor?

Im assuming this would be the simplified one

ld = (fy*φt*φe*φg/1.4λ*root(f'c))*Db

the one where may aplly for a reduction

ld = fy/1.1λ*root(f'c)*φt*φe*φs*φg/((cb+kr)/db)

the fy = would be the maximum yield strength of the steel?, or is the fy dependent of the occuring force?

 

[BulbTheBuilder]

Is the development length independent of the force that acts on the anchor?

yes, the development length is independent of the force on the anchor.
However, you should have enough reinforcement for tensile or compressive stress within that zone.

Im assuming this would be the simplified one
ld = (fy*φt*φe*φg/1.4λ*root(f'c))*Db
the one where may aplly for a reduction
ld = fy/1.1λ*root(f'c)*φt*φe*φs*φg/((cb+kr)/db)

Yes, that's correct

the fy = would be the maximum yield strength of the steel?, or is the fy dependent of the occurring force?

fy is the yield strength of the rebar. Assuming you're using 460MPa or 60ksi rebar, your fy=460Mpa(60ksi) for computing the development length.

Now if the embedment length is lesser than the development from the above equations then you proceed to use fy (maximum yield that can be achieved with your current length) to develop your anchors. Example, say i need 17"(431.8mm) to develop #8 (25mm) rebar 60ksi(460MPa) but it is only embedded 12" (330.2mm). I will use fy of 12/17 (60) = 45.88ksi [330/431*460 = 352MPa) to compute the area of steel required.

[EDIT] : I forgot to plug Celt83's website tool here. You can check out the link below for development lengths.

https://thestructuraltoolbox.com/concrete/aci_development

 

[Robin1020211]

Thank you very much for your answer!

Because we actually never work with the ACI here in Europe, it's difficult to verify if my calculations/findings are correct, so I want to thank you once again!

Furthermore, I am also comparing the lap splice length of reinforcement bars. In section 25.5.2.1 of the ACI, I see that this relates to the required reinforcement and the provided reinforcement. So if I understand correctly, with the simplified method, you can make a rough, quick calculation, and with the detailed method, one can achieve a reduction (like in EC2) in the anchorage/splicing length.

 

[BulbTheBuilder]

You're welcome, Robin1020211. Glad I was of help.

Fun fact, I learnt BS 8110 when I was school. Then learnt EC2 on my own when I started working and had to learn ACI 318 on my own when I moved to North America. It been a while since I used EC2 so i don't remember much.

Furthermore, I am also comparing the lap splice length of reinforcement bars. In section 25.5.2.1 of the ACI, I see that this relates to the required reinforcement and the provided reinforcement. So if I understand correctly, with the simplified method, you can make a rough, quick calculation, and with the detailed method, one can achieve a reduction (like in EC2) in the anchorage/splicing length.

You are correct

Yes, table 25.5.2.1 relates tension lap splices to development length, and you can make rough and quick calcs with those.
The development length can be computed based on the two methods; simplified (table 25.4.2.3) and detailed method (25.4.2.4).


If i may ask, why are students in Europe using ACI ?

 

[Robin1020211]

Thank you very much again!


We students normally don't use ACI but Eurocode 2 haha, however, I am currently engaged in my thesis research where I compare international standards with Eurocode 2, particularly focusing on the differences in ductility.

So far, most of the differences are in field of seismic resistant construction where ACI and NZS set high requirements for ductility, which makes sense, since seismic activity is much higher in those countries!

Edit:

Since I am finishing my research with the ACI, I am encountering an issue with the NZS. I am having trouble finding how and where the design of a reinforced concrete beam is addressed in NZS 3101. Perhaps someone could help me with this?



Robin