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.

 

[dik]

Bigger problem is the placing and segregation of concrete.

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

-Dik

 

[FirmFound]

Yes, Lex, indeed it is far too tight, they are using a concrete mix with 3/8 pea gravel on the pedestals, which helps. At a minimum the additional length of the tail is totally redundant. In addition to the overkill of closed inner ties. There are top, mid, and bottom corner bars for grade beam interface with pedestal and (4) #6 U-bars for the anchor bolts. Could all this be for wind shear in hurricane zone? The steel frame building that this pedestal supports is approx 30' tall.....

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

 

[FirmFound]

The funniest thing about all this is the general note that says to "alternate ties in successive layers."

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

 

[Just Some Nerd]

Why the closed tie design on the interior?

Idea I had in mind looked more like this, for clarity....

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

 

[dik]

Or from a while back:

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/raw/upload/v1696480033/tips/Column_kzrgdg.dwg[/url]

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1696480034/tips/Column_wv6yqa.pdf[/url]

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

-Dik

 

[lexpatrie]

I think at minimum the 180° tie bends are "seismic" and the 90° or 135° bends would be more typical for a wind controlled design.

I kind of think all of these schemes look funky. I don't remember every vertical needing a 90 degree tie bend next to it.

That bit about flipping the ties around also feels very seismic.

 

[FirmFound]

Right guys, I agree totally agree and am very used to these designs and have installed and inspected many myself, I myself not being an engineer but self admitted powerful lust for knowledge of how and why things work. The kid the disassembled and reassembled everything!!! I've built much bigger and taller structures with more proportionate reinforcement. This is the first pipeline compression station I've had the pleasure to build, first native soil supported foundations I've built. My experience has been in heavy industrial, 65-120ft pre-cast concrete or auger-cast piling supported structures. Anyway, thanks for all the feedback guys, I'm most thankful that no one was able to provide a spec reference that would drive the need to alternate such ties, I feel armed for battle with a QA's personal preference.

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

 

[dik]

I've only done a couple of RC structures in a seismic area... most of my work has been non-seismic. I've flipped the ties for all work for decades... it's standard on projects of I've designed.

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

-Dik

 

[Just Some Nerd]

That bit about flipping the ties around also feels very seismic.

If dealing with seismic, I wouldn't be messing around with 90 degree hooks at all.

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