Correct lapping zone of Rc Columns in Seismic Areas

[kellez]

I was very surprised today to learn from my new supervisor, a senior civil engineer that the correct lapping zone for RC columns is at mid-height of the column (where bending moments are lowest)and not at the bottom as i knew until today. To be honest, in my country Reinforced Concrete is the traditional way of construction and i have never seen lapping zone at mid-height. I havent been on a lot of projects but all projects i have seen lapping zone was at the bottom.


so what do you think about this and what is the common practise in your country, also what to american standards suggest for this?

 

[basil29]

For SMRF in Seismic Areas, location of lap splice for columns shall be near midheight. You can refer to ACI 318-14 Section 18.7.4.3.

 

[HTURKAK]

This is common practice for high seismic zones. Pls look to :

https://nvlpubs.nist.gov/nistpubs/gcr/2016/NIST.GCR.16-917-40.pdf

Seismic Design of Reinforced Concrete Special Moment Frames.A Guide for Practicing Engineers.

 

[Agent666]

It's a similar requirement in New Zealand. In fact I don't think I can recall any recognised international standard that says otherwise.

It's not just about getting it to a point of low moment. It's more about getting it away from any potential yielding regions, these might extend 2 to 3 times the member depth from the ends of the columns in a typical RC moment frame.

 

[Klitor]

Offcourse we are talking about pure ec8 moment frame (a rare beast imho).
In wall system, splice wherever you want.

 

[Lomarandil]

Exactly -- it's the balance between:

High seismic zones, where column ductility and shears are critical -- splice at mid-height.

Low seismic zones, to reduce costs by making the splice elevation readily accessible by workers -- splice at the bottom.

----
just call me Lo.

 

[kellez]

Thank you everyone for your comments, i like it when i learn something new.

However we have two suggestions here, Klitor is saying that only in pure moment frames we have to use lapping at midheight, while everyone else responded in general that in high seismic areas we have to use lapping is at midheight.

To be honest in most high seismic areas buildings of 2 storeys and more always have shear walls, therefore making it a wall system, which then means that you dont have to use lapping at midheight. Can anyone comment on this?

 

[KootK]

In my experience:

1) For low seismic areas, it's lapping at the floor level.

2) For high seismic areas and columns not designed to be elements of moment frames, it's lapping at the floor level.

3) For high seismic areas and columns part of ductile moment frames, it's lapping at mid-height.

The mid-height lapping is important where it applies but you should not be under the impression that all, or even most of the columns that you'll encounter will be detailed that way. Your past experience of seeing column bars lapped at the floor level should still apply to most situations.

 

[Enhineyero]

Kellez, If this is on a particular project ask the structural engineer about what type of lateral system they used for the design (they are going to be surprised!). It might be a dual system, moment frame + shear wall.

 

[kellez]

Ok thank you everyone, now its more clear.

Enhineyero, why would the structural engineer be surprised if asked him about the structural system?