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anchoring rebars in foundations

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gmd255

gmd255

Structural
Apr 17, 2017
49
SI
Im more of a steel/wood guy, so I hope i ll get some feedback about this topic.

What is the proper way to anchor rebars in foundation? Im from EU so Im using Eurocodes.

In a case of large single foundation we can get bend (L shape - 90 degrees) rebars since there is enough space in foundation to do that.
But what about small foundations where there is no space for L shape rebars? I want to avoid welding anch. plates and stuff like that. Is it OK to make U shape rebars anchoring instead of L shape?

As I said thats not really my field. I have been studying Eurocodes regarding this but i have found out that effective anch. lenght that I can consider does not include horizontal part of L bend rebars but only vertical part... i dont get that... Why cant we consider that rebar is fully anchored as soon as we bend them so we have a hook or L or U shape rebars? Especially when it comes to foundation where there is a lot of concrete above bend part of rebar? Also if we cant consider horizontal part of L shape rebars (X in picture), what is the purpose to even bending them?


LARGE_lrsaxg.png



SMALL_mfaohd.png



Anchoarage_Length_requirements_ksslt5.jpg
 
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It depends on how your are utilizing the column rebar. Are the bars subject to tension or compression only?

1) If the bars are subjected to compression only, then you want standard length hooks turned outwards. The hooks don't actually do anything to improve anchorage in this situation as pushing on a hook is pretty useless. You get large bearing stresses around the bend and the hooks tend to spall out the concrete on the back size. So you'll design your anchorage length based on the straight portion of the bar and ignore the hooks. You'll still keep the hooks in the real world though because they make it easier to stand and secure the column starter dowel cage.

2) If you need to use your column bars in tension, then something like B or C is appropriate as it suites the mechanics of these joints to have the bars turned inwards.

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.
 
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I've used U bars and they work well and are easy to place and secure.

The bend should be in the direction of the compressive load (in the concrete) to further clamp the bar in place. Your detail a) is what I normally use; it doesn't matter if tension or compression bars.

Dik
 
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