Tension Connection for Concrete Filled Steel Pipe Pile

[ramu2krism]

I am reviewing a tension connection detail for 12"OD steel pipe pile filled with concrete.It is common practice welding rebar to the pipe pile for tension this type of connection, Customer wants to avoid welding rebar to the pipe or any type of connection detail which involves welding. They provided a detail with 4-#8 bars embedded in to the pipe pile filled with concrete upto 3 foot with a hook on the other side of the rebar, which would eventually run in to the pile cap.

Since the load transfer occurs completely through bond, they used Eq: I 9-9 from AISC 14th Ed Section I 6.3c to check the tensile strength of the connection, from the load transfer throgh the bond between concrete and inner surface of the steel pipe pile.

- Does the equation mentioned above from AISC is applicable for the condition.
- Has any one ever used or come across tension connection detail for concrete filled steel pipe pile which does not involve welding.

Your response would be truely appreciated.

Sincerely,
krism

 

[hokie66]

There is this research, but it is for bridge bents, with piles embedded into the capping beam. The authors do mention other research where the piles are not embedded.

https://www.mdt.mt.gov/other/resear..._proj/seismic/phaseiii/final_report_jan13.pdf

 

[MacGruber22]

KootK, after reading the Canadian research report and scouring the internet, I am convinced (at the moment) that the current AISC provisions are not intended for pulling a concrete plug out of a tube (as the OP describes). The difference in average ultimate bond strength is quite different between AISC (0.40 MPa) and the Canadian report (4.25 MPa).

I believe AISC axially-loaded composite filled tube provisions are based on:
1. Fully-filled tube
2. Tube acts primarily as a compression member

As you said, the shell dilation seems to provide a significant clamping force resulting in a much larger average shear stress than in the AISC code. It seems you lose this clamping force when the tube is fully-filled. This of course is highly dependent of whether the Canadian researchers were drinking and eating copious amounts of poutine at the time they were writing their report.



"It is imperative Cunth doesn't get his hands on those codes."

 

[hokie66]

Well, they weren't Canadians. They were Australian as I pointed out to KootK, so it would not have been poutine.

 

[thaidavid40]

I have to confess confusion regarding the forces acting in this situation. Wouldn't the tension on the extended rebars be transferred to the concrete "plug", extending all the way to the bottom of the bars (and ostensibly, to near the bottom of the plug)? If that is so, then wouldn't that tension resolve itself as a force in the concrete spreading upwards at a 45-degree angle, until it intercepts the I.D. of the pipe (like the force distribution on an anchor rod)? At point, wouldn't the force cause the concrete to be compressed against the inside wall of the pipe, thus increasing (not decreasing) the bond, due to the circumferential frictional pressure on the pipe's inner wall? I suspect that this is the reason the Coloradans have success with their pipe piles, while so much of the detailed analysis seemingly calls that into question. I have never had an occasion yet to use such a detail, but the more I think about it, the more I am inclined to consider definitely using it when needed.
I'm not sure what the Coloradans' favorite dish is, but reading this post has made me hungry for steak.

Thaidavid

 

[KootK]

You know, I have yet to try poutine. I'll have to get on that. As far as I know, it is Canada's lone contribution to the world's culinary cuisine stock.

after reading the Canadian research report and scouring the internet, I am convinced (at the moment) that the current AISC provisions are not intended for pulling a concrete plug out of a tube (as the OP describes).

That is my impression as well. However, given how wildly conservative the AISC provisions appear to be, using them surely doesn't result in any harm. The paper mentioned some relevant BS standard provisions. If any Brits catch wind of this thread, I'd love to hear about those provisions.

But, regardless...I still don't see the bond strength equation in chapter I providing the capacity unless the tension demand is not anywhere near the area of steel provided by 4#8

...and...

If that is so, then wouldn't that tension resolve itself as a force in the concrete spreading upwards at a 45-degree angle, until it intercepts the I.D. of the pipe (like the force distribution on an anchor rod)?

As you've both touched on, the question of how the joint should be designed is an interesting one.

1) In some respects, the joint is a non-contact lap splice between the rebar and the walls of the CHS. This would favor vertical rebar fairly close to the walls of the CHS.

2) I question the researchers supposition that there are meaningful, tensile Poisson effects in the concrete plug. Like David, I see the concrete cracking in tension, transferring all of it's tension to the rebar, and therefore not really contracting under tension.

3) If a strut and tie style mechanics were to develop, as David has proposed, then the struts would indeed cause a form of dilation in the concrete plug. In a sense, this would favor placing the vertical bars closer to the center of the connection as that would increase the lateral thrust against the walls of the CHS.


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.

 

[MacGruber22]

Sorry...Vegemite it is.

KootK - I hear you about the conservative nature of AISC. Though, something still seems off even that being usually true. The good thing is that there is no restriction for US engineers grabbing techniques from outside the states as long as there is data to back it up.

1) and 3) conflicting makes this much more difficult to rationalize without good testing. It seems that pipes/tubes with high D/t ratios would be better suited to behave like 3), and those with low D/t ratios would require the transfer to be completed via 1).

That strut has to occur very earlier, or else brittle slip is likely. If ramu2krism's 12" pipe has a heavy wall, that could be a problem. Then again, you have to have the data to distinguish between the good, the bad. and the ugly.

I am eager for ramu2krism to chime in...

"It is imperative Cunth doesn't get his hands on those codes."