Alternating 180 degree cross-ties? 5

[FirmFound]

Hello all, I am aware of the need to alternate the ends of the 90/135 hooks, on this project all of the cross ties are detailed with double standard hooks of 180 degrees, and the general notes states, "Location of hooks and direction of hairpins shall be alternated in subsequent layers." This raises a few questions for me:

1. Does ACI call for such alternation on 180 degree hooks?

2. Would that alternation consist of the continuous "leg" of the tie on the opposite side of the longitudinal bar in successive tie sets?
3. How would such an alternation benefit the designed purpose of the hairpin?

I ask because as I understand the reading of the commentary in ACI 318 Chapter 25.4 Development of reinforcement.

R25.4.1.1 The development length concept is based on the attainable average bond stress over the length of development of the reinforcement.

If the "strength" of the tie is based on the bond stress of development of deformed bars, what purposed would be served by alternating from one side of a longitudinal bar to the other? It would be the only way to alternate a double 180 degree standard hook, to flip it end for end places the tie in the same position. Hopefully my explanation is properly conveyed, have you ever encountered or addressed a similar issue, any help would be greatly appreciated.

 

[Lomarandil]

I also don't see the purpose in this, and I'm not aware of any ACI requirement driving it.

 

[dik]

A question... are the dimensions such that you could do the attached? Seems like a lot of rebar (could be seismic issue) to prevent concrete placement. Double 180 hooks on ties make them difficult to place.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[JLNJ]

If you have less than 6" between bars you can eliminate the ties, right? Maybe the whole thing can be simplified.

 

[dik]

some of them... I think... I'm not really big in concrete... just from old memories... seem to recall 6" from a supported bar...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[BridgeSmith]

seem to recall 6" from a supported bar...

That's how the AASHTO provisions read. I think everything in AASHTO is 12" or 24", though, so, we can go up 48" horizontal spacing for cross-ties in some instances.

Double 180 hooks on ties make them difficult to place.

Very difficult...somewhere between swearing-at-the-engineer-all-day-long difficult, and we're-not-even-going-to-bid-the-job difficult. That's why the spec mentions alternating 90 and 135 degree hooks.

Btw, since they're symmetrical, how would you alternate cross-ties with 180 degree hooks on both ends, anyway?

 

[FirmFound]

Thanks for all the responses, seismic is doubtful, we're in SE Texas, not sure if it matters, but none of the job is pile supported and it's a pipeline compression station if that matters. The job is in progress, just came on as QC and pretty sure QA will require RFI'$ for clarification. I think it could possibly be a cut and paste scenario from some engineer that was in autopilot and figured....
Cross ties=Alternation.

It's not what you know, it's what you can prove.

 

[dik]

Just recalled... not certain or what code changes have occurred... been 20 years since I last did a significant concrete project... The only concrete work I do is some small slabs and/or gradebeams...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[dik]

... have the hooks facing the opposite direction?

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[FirmFound]

dik

... have the hooks facing the opposite direction? ponder??

This is an idea I posed in the original post, and asked if being on the opposite side of a longitudinal bar benefitted the design strength.

[highlight #FCE94F]2. Would that alternation consist of the continuous "leg" of the tie on the opposite side of the longitudinal bar in successive tie sets?[/highlight]

It's not what you know, it's what you can prove.

 

[dik]

... was just joking, but offering an answer to the question.

I'd use (and have used) alternating 90-135 bars for decades... that's why I suggested them in the first place.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[FirmFound]

Right, I apologize for snapping at you... Lol

Everything here is engineer approved and fabricated, and I do remember reading in ACI where it talked about the uneconomical use of such hairpins, thanks.

It's not what you know, it's what you can prove.

 

[dik]

No offense taken... just thought I may have confused issues... My humour is funny (in a different sense) sometimes and not always appreciated.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[FirmFound]

And I've been told I need to lighten up, I usually enjoy humor in hindsight, maybe I'm too literal.

It's not what you know, it's what you can prove.

 

[Just Some Nerd]

I would have preferred larger bars with an even number on each face to allow only using closed ties...much neater in that regard. Would also still reduce the number of bars even if not using closed ties to save time on site and avoid some of the effort installing so many inner ties.

180 degree hooks however are not too hard to install in my experience, and have not had issues with on many jobs with it (particularly recently, I think the industry here got used to it) provided there isn't too many for the size of the column. Often steel fixers ruin it by being lazy and not wanting to fix their mistake when they don't alternate them properly... I'm a bit jaded over that happening in the past.

----------------------------------------------------------------------

Why yes, I do in fact have no idea what I'm talking about

 

[FirmFound]

Thanks, Just Some Nerd, agreed, I think the rodbusters unwillingness to fix such mistakes just shows their lack of planning and attention to detail or maybe just plain ignorance...."There's never time to do it right, but always time to redo it."

On another note, and back to my original query, it occurred to me last night as I continued to build this project in my mind while laying down to sleep, the apparent over design of this project must be due to the fact that we are in a hurricane zone and just 3 years ago were hit with a category 5 storm named Laura, which caused irreparable damage to the area. With that said, I leave all you engineers with this screenshot to ponder and comment on if you like.

I do have a question about it though, Why the closed tie design on the interior? 1 tail is standard length and the other overlaps it by approx. 1/2 inch....This has created some installation challenges to say the least, obviously built from bottom up, all ties installed oner the top of the longitudinal bar up to the bottom of anchor bolt. Then anchor installed and rebar completed around them, OUCH!!!!!

It's not what you know, it's what you can prove.

 

[dik]

Those ties are not an improvement, in any manner.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[FirmFound]

Indeed dik, rapidly approaching a hellscape!!!!

It's not what you know, it's what you can prove.

 

[dik]

That was in an eMail my son sent me a year or two back... I liked it, so asked his permission if I could use it as a tagline. I'm not really big on concrete, but about 40 years back, I worked for 10 years with one of the better reinforced concrete consultants in Canada.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[lexpatrie]

FirmFound that looks like a detail from Harbour Cay, except with extra bars as ties.

Is that vertical rebar beyond 4% or 8% let alone the congestion of the ties (*not* hairpins), how does any of that meet clear spacing for passing wet concrete? 1/16" maximum size "coarse" aggregate?

Regarding the OP, ask them (RFI) to re-evaluate the tie requirements. Clear spacing looks tight, visually.