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Tension transfer from concrete

Tension transfer from concrete

Tension transfer from concrete

(OP)
The figure attached below shows a fixed pile cap. The moment from pile cap has is has to be transferred to the pile re-bar embedded in the pile cap.
How the moment from pile cap would be transferred to the pile re-bar.

1 Can concrete transfer tension from the pile cap to pile re bar.
2 Does the pile cap carries the entire moment and the moment is transferred through push and pull action of the pile re-bar.
3 It is possible that the links around the pile cap wont allow the concrete to crack and would transfer tension from pile cap to pile re bar, Unfortunately the links are not so closely spaced.

Please explain me the best possible solution with justification.

https://res.cloudinary.com/engineering-com/image/upload/v1439580065/tips/Tension_transfer_plrjzw.pdf

RE: Tension transfer from concrete

(OP)
I would be grateful if somebody take a step to reply my answer.

RE: Tension transfer from concrete

1 Can concrete transfer tension from the pile cap to pile re bar.
Yes, that is common practice.

2 Does the pile cap carries the entire moment and the moment is transferred through push and pull action of the pile re-bar.

Not entirely. The tension is transferred through the pile rebar on the tension side. The compression is transferred mostly by concrete in compression but the bars will have some compression as well.

3 It is possible that the links around the pile cap wont allow the concrete to crack and would transfer tension from pile cap to pile re bar, Unfortunately the links are not so closely spaced.

The links should be spaced in accordance with the code.

BA

RE: Tension transfer from concrete

(OP)
Put it this way ,
The pile rebar has enough development length so it stays inside the concrete by bonding action .
Since now that the pile rebar and pile cap as connected firmly they act together so now the moment would be transfer to the pile cap vertical U bars as push and pull force. The above behavior is based on the assumption that the links are not effective in transferring tension force from concrete to pile rebar and pile cap U bar.
Kindly clarify me if I am wrong

RE: Tension transfer from concrete

(OP)
I was wrong earlier,if the tension from pile is not transferred through the concrete to the pile rebar the system collapse.
Either I have to increase the pile rebar embedment or the links must be placed closer according to transfer tension from concrete.

RE: Tension transfer from concrete

This would seem to be the continuation of this thread: Link. I posted the sketch below there as part of the recommendations provided. You seem to have followed some of those recommendations with your revised detailing which is great. You also seem to still be resisting the concept of a more direct lap between pile rebar and column anchor bolts which is not so great. More on this later. In the other thread, you claimed that you couldn't do this because of anchor bolt / pile rebar interference issues. I don't get it but will work to the parameters that you've specified.

Quote (OP)

1 Can concrete transfer tension from the pile cap to pile re bar.

It sounds like your simply describing rebar developement which can, of course, be relied upon. That's just one element of a properly designed connection, however, and a pretty non-critical one at that. The other elements of the connection are implied by the sketch below.

Quote (OP)

2 Does the pile cap carries the entire moment and the moment is transferred through push and pull action of the pile re-bar.

Agree with BA here. You could take your flexurual compression forces through your compression side rebar alone but it's generally more practical to use your compression side concrete for that purpose as shown in the sketch below.

Quote (OP)

3 It is possible that the links around the pile cap wont allow the concrete to crack and would transfer tension from pile cap to pile re bar

Yes but I would rephrase that to: is it possible that links around the pile cap will allow tension in the pile cap rebar to be transferred to pile rebar via a non-contact splice using the interstitial concrete as a tied compression strut..

Quote (OP)

Unfortunately the links are not so closely spaced

This is the tricky bit. And it depends what approach you are taking. You are essentially making non-contact lap splices at both the top and bottom of the pile cap and both need attention.

At the top of the cap...

I consider this to be the weak link in your current version of this connection. You've got some links up there which reflect the upper tie shown in the sketch below. That's great but I question whether or not your nelson studs extend far enough into the pile cap to really engage your pile cap vertical rebar.

How was the embed plate and stud assembly designed? Does it need to form a non-contact lap with the pile cap vertical rebar or was it designed assuming unreinforced concrete using ACI 318 Appendix D principles? If it's the latter then a) I'm surprised that it works and b) if it works, you may have a much simpler connection design option available to you (let us know).

There are a few more issues consider regarding the embed plate instead of traditional anchor bolts:

1) You're pretty much forcing the contractor to wet set the plates which raises concrete quality concerns in the most important region of the joint. I wouldn't do this in an important connection.

2) Welding a column to an embed can be done but it's not easy. Plumbing the column is tricky and you can expect your embed plate to be two inches out of place and 15 degrees out of level.

At the bottom of the cap...

You've provided U-bars which you've probably intended to supply the lower pile cap tie shown in the sketch below. That's great and, using that approach, the bend in the U-bars would need to be designed using something akin to the curved bar node strut and tie method (Link). The European codes have different ways of dealing with this.

Another, possibly simpler way to deal with the lower bar splice is to let your links function as the lower pile cap tie. In this case, your links must be spaced such that they properly tie the compression strut that would form between the non-contact lapped bars. If you only need to engage the corner pile cap bars, then your current tie arrangement would be fine and you'd only need to play with the spacing. If you need to engage all three corner pile cap bars, then you would need to use a tie arrangement similar to what you're using at the top of cap in order to restrain all three bars. And, obviously, those links would interfere with your pile rebar quite badly. Far more than lapping anchor bolts likley would.

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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