Mechanical Coupler in SMF, more than 50% splice allowed? 4

[NewbieInSE]

Hello Engineers,

Thanks.

 

[HTURKAK]

As per the figure you haave posted,as far as I understand, at any section ,50% of bars allowed to be spliced.. and the vertical distance between splices 600 mm or more..
You may consider splicing of longitudinal column reinforcement every other floor to reduce congestion and make economy..

Just curious, where did you find this figure ?

I will suggest you to look ;

https://www.nehrp.gov/pdf/nistgcr8-917-1.pdf

 

[BridgeSmith]

We have a similar limitation in the AASHTO spec, and I understood it was so that, in a large seismic event, the continuity of all of the bars would not be lost if the concrete spalled away. If that is the reason, there would be no need for mechanically spliced bars to be subject to the 50% limitation.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[NewbieInSE]

Thanks HTURKAK and BridgeSmith for responding.

HTURKAK, Its a snapshot from BNBC-2020 (BANGLADESH NATIONAL BUILDING CODE-2020) which actually follows ACI, AISC, ASTM, AWS, AASHTO etc. I'll try to attach the pdf file for your information.
BridgeSmith, My boss said, in SMF if mechanical splice is used then more than 50% splicing can be done in a story. Because Code says, alternate bears can be spliced at a section, and another section has to be 600m above or below. So at the other section i might splice alternate bears again.

 

[NewbieInSE]

Link

Download link is given here. I'm just sharing it, it contains a lot of things from here and there(though brief).

 

[NewbieInSE]

I wanted to know whether what my boss said is practiced internationally.

 

[HTURKAK]

The subject code states (...not more than alternate bars may be spliced at any section with vertical distance between splices 600 mm or more )..

- Max. 50% may be spliced at any section..provide 600 mm or more vertical distance between splices
- All of the longitudinal bars may be spliced in a storey ..

IMO, your code is more stringent than other international codes...

 

[dauwerda]

Here are the requirements from ACI 318-14 for a column in a special moment frame:

18.7.4.3 Mechanical splices shall conform to 18.2.7 and
welded splices shall conform to 18.2.8. Lap splices shall be
permitted only within the center half of the member length,
shall be designed as tension lap splices, and shall be enclosed
within transverse reinforcement in accordance with 18.7.5.2
and 18.7.5.3.

18.2.7.1 Mechanical splices shall be classified as (a) or
(b):
(a) Type 1 – Mechanical splice conforming to 25.5.7
(b) Type 2 – Mechanical splice conforming to 25.5.7 and
capable of developing the specified tensile strength of the
spliced bars
18.2.7.2 Type 1 mechanical splices shall not be located
within a distance equal to twice the member depth from the
column or beam face for special moment frames or from
critical sections where yielding of the reinforcement is
likely to occur as a result of lateral displacements beyond
the linear range of behavior. Type 2 mechanical splices shall
be permitted at any location, except as noted in 18.9.2.1(c).

18.2.8.1 Welded splices in reinforcement resisting earthquake-
induced forces shall conform to 25.5.7 and shall not
be located within a distance equal to twice the member depth
from the column or beam face for special moment frames or
from critical sections where yielding of the reinforcement is
likely to occur as a result of lateral displacements beyond the
linear range of behavior.

25.5.7 Mechanical and welded splices of deformed bars in
tension or compression
25.5.7.1 A mechanical or welded splice shall develop in
tension or compression, as required, at least 1.25fy of the bar.
25.5.7.2 Welding of reinforcing bars shall conform to
26.6.4.
25.5.7.3 Mechanical or welded splices need not be staggered
except as required by 25.5.7.4.
25.5.7.4 Splices in tension tie members shall be made with
a mechanical or welded splice in accordance with 25.5.7.1.
Splices in adjacent bars shall be staggered at least 30 in.

 

[NewbieInSE]

I think, I had mistaken about the spacing of 600mm. As HTURKAK said that the code says 600mm distance is between the alternate splices in a row or layer of rods. So if I have 5 bars in a layer and assuming that the corner bars will go without splicing, i can spice 2 rebars (2nd and 4th bar) in that layer. The spice distance between these two bars has to be 600mm. This 600mm is not between the multiple sections which I had thought first.
Now, can I splice bar no. 3 going some more up by say more than 600 mm?
What does the code mean by 'at a section'? Can I have multiple sections for a column in a story.
If I'm to splice more than 50% rebar by mechanical spices, then I have to have two sections in a story.
If 'at a section' means 'in a story', then it by default means I can go up to only 50% splicing by splicing the alternate longitudinal bars at a section.
I would be glad if you clarified my confusion.

 

[NewbieInSE]

. All of the longitudinal bars may be spliced in a storey

Would you please tell How you made this conclusion?

 

[dauwerda]

This is my interpretation of your initial post:

 

[HTURKAK]

Mr DAUWERDA nailed it and a pink star for him.. The picture that you posted shows the welded or mechanical splices on the same storey and if you splice the alternating bars , literally max 50% of bars spliced at any section for rectangular columns with symmetrical reinf.

Personally i prefer splicing of rebars at every other floor to reduce congestion and make economy..

 

[NewbieInSE]

Thank you Mr. HTURKAK and Mr.dauwerda for your efforts in clarifying the issue. I'm glad.