Anchorage lengths for straight and bent bars 1

[Alan CA]

Hi,

I realized in the Eurocodes that the anchorage lengths required for bent, hooks and loop bars are larger than the lengths required for straight bars!
I would imagine that the opposite should have been required! A straight bar needs a larger anchorage length than a bent of hooked bar which, the latter, can hang on in concrete far better. Why the Eurocodes (and maybe other codes) require larger anchorage length for bent rebars?

 

[TehMightyEngineer]

I'm not familiar with the eurocodes but you must have something mixed up as hooked bars should have a significantly shorter development length compared to straight bars.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[Alan CA]

Thank you for answering my question. Actually, I don't think my observation is wrong. Please check this anchorage table from the Eurocodes for beams and slabs anchorage. Please give me your opinion. You can find a print screen of the table attached in my comment.

 

[TehMightyEngineer]

That table is just confusing in multiple ways to my understanding. Hooked bars are not good for developing compression and ACI 318 specifically does not let you consider the hook for compression development.

If that table is correct then why would anyone ever hook rebar?

Like I said, not familiar with EC2. As best I can tell α₁ is the factor applied to the basic development length l_b,rqd and for other than straight per EC2 Table 8.2, α₁ = 0.7 if you have sufficient clear cover for the bar. Thus, a proper hooked bar should have a lower development length per EC2.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[hokie66]

It looks like they need to define "good" and "poor", as they don't seem to have the usual meaning.

 

[TLHS]

There are modifiers for the hooks but there are also modifiers for cover. Hooked bars have greater cover requirements than straight bars. Looks like the modifiers might be cancelling out for this case. The simplified method gives you straight bars with a 0.7 reduction for having sufficient cover. The hooked bars give you 0.7 reduction for being hooked but a 1.0 factor for cover because of the increased requirements.

Might be wrong on the details. Only touched Eurocode a few times.

I think you can also use more advanced equations and start doing things like using longer hooks and then count the bar length around the corner.

 

[TLHS]

Yeah, it's stacking modifiers. See the tables explaining the various alpha modifiers on this page

http://www.structville.com/2017/07/how-to-calculate-anchorage-and-lap.html

The modifiers end up treating hooks really poorly on small amounts of cover.

I think that for hooks it's just the side cover that counts, though (I would need to look that up). The worry being something like sideface blowout, I presume.