Strut-Tie - Tie Development at Nodes (Starter Bars) 2

[BacBac]

Reviving this thread:

Strut And Tie - Tie Development At Nodes - Structural engineering general discussion

Hi All, Looking for some input on how you all handle ACI requiring tension ties anchorage at nodes. ACI Section 23.8.2 states Tie reinforcement shall be anchored by mechanical devices, post tensioning anchorage devices, standard hooks or straight bar development in accordance with 23.8.3 (Tie...

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Does anyone have any ideas on how to justify the starter bars reinforcement is developed at the node?
For the shear ties, reference from Australian Standards, it's said to be fully anchored if shear ties detail is followed (AS3600-2018 clause 12.2.1 that refers back to Clause 8.3.2.4 for anchorage of shear ties).

However, nothing is referred for the development of the starter bars of the column.
Any help would be appreciated
Thanks!.

 

[KootK]

But I guess OP could place transverse bars to decrease the anchorage. Does that work?

I suspect not if it's the arrangement that I'm thinking of. In ACI, those are often termed "supplementary reinforcement". It runs across the breakout frustum and gives a pretty modest increase in capacity. Something like 15% if I recall correctly.

 

[KootK]

But generally speaking a hoop can only fail by bursting in a perpendicular direction

I feel that the most important failure mode of a hoop will usually be the development of a breakout frustum. Obviously, the fact that a hoop is perfectly developed does not obviate such a failure mode.

Eurocode (if I'm interpreting it correctly) says that a hoop is by default anchored, no need to check it. Leonhardt said something like anchorage length = 3D so it is a huge difference to the standard hook.

Can you direct me to that information (clause / section)? I have access to Eurocode and a lot of Leonhardt's stuff.

 

[hardbutmild]

@KootK I'm sorry, I don't feel like adressing all of your comments. It may be bad etiquette, but I just feel like we're missing each others point.
I think I just realized you're talking about no stirrup solution and I was thinking that OP drew some stirrups there. I never used or even saw a foundation beam without stirrups, just mats.

Can you direct me to that information (clause / section)? I have access to Eurocode and a lot of Leonhardt's stuff.

Sure. In Eurocode 1992:2023 (so the second generation) clause 11.4.6 (1) is: "For U-bar loops subject to pure tension, anchorage may be considered to be provided if the loop details comply with 11.3."
Section 11.3 is titled "Permissible mandrel diameters for bent bars" and deals with avoiding crushing inside the bend.
To me this phrasing seems that loops are anchored by default (of course if you have a large enough mandrel), but if you feel like looking it up I would love to hear your interpretation of the clause.
In Leonhardt - Vorlesungen uber massivbau teil 3 figure 4.14. suggests that a loop is anchored 3D from the end of the bend, it's section 4.3.3.1. I read the text around that figure, but my german is not very good so I may have missed something crucial.

You talked about what you consider as a loop vs "what I maybe consider". It should be the same unless you're again talking about a length of 1 km between the bends. There is an article from the same authors that I posted that tested both versions of loops and it seems that the one with straight part performed better.
In the new eurocode 1992:2023 (so the second generation) clause 11.3 (4) states: "In case of multiple bends, the length of the straight sections between bends shall not be shorter than 4ϕ.", but says nothing about the presence of that straight part either improving or reducing anything.

As to your last figure, based on the Leonhardts drawings (see earlier in my post) and text, he's suggesting that failure occurs in a perpendicular direction and that makes more sense to me. Basically it's like cutting the cheese with a string, it'll split in the plane of the hoop so tension is in the perpendicular direction.

Sorry for not adressing all of your comments, I just feel like we're getting out of hand and that there is a lot of misunderstanding.

 

[human909]

I've only just stuck my head into this thread. And there is some good stuff here. And it isn't just good discussion about STM models and development lengths (which are two things that I need to better 'develop' my skills in.

We also have pictures of guillotines, of Kootk bending over to drink from a fire hose and the very specific and vivid image of "KootK, Dog, & Sons says that same thing, you shove those same dowels up KootK's backside and tell him to get bent."

Great stuff!

While I have zero experience working in any consultancy firms but I certainly have dealt with them. Like all organisations they are subject to group think and they can readily be 'wrong' about things. As Kootk says the incentives are just different.

In my work I provide, review and even procure structural services. There are plenty of big consultancy firms with poor engineers (engineering).