Is there any limit of distance of longitudinal reinforcement in columns 1

[Pretty Girl7]

I didn't notice that the eurocode have any limits of the distance of longitudinal reinforcement in columns. I'm not talking about links (transverse), I'm talking about the main long bars in the columns.

As I see the calculation of reinforcement required (ASreq) only provides the area of reinforcement. But the area can be provided in many ways as follows. But there should be a distance to the reinforcement isn't it, or else anyone would just provide it just on the four sides of the column.

Are the limits mentioned in the Eurocode?

 

[GeorgeTheCivilEngineer]

Check out 'surface reinforcement' covered in Annex J of EN 1992. Not sure it directly applies to columns but starting point I guess?

Edit - also cl 9.6.2 (3) for walls could be a sensible application if your columns are quite 'wall-like'. Spacing not exceeding 3x the lesser dimension (thickness for a wall).

 

[HTURKAK]

Pls look clause 9.5.2 Longitudinal reinforcement for columns

and ,

9.5.3 Transverse reinforcement

(6) Every longitudinal bar or bundle of bars placed in a corner should be held by transverse reinforcement. No bar within a compression zone should be further than 150 mm from a restrained bar.








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[Pretty Girl7]

if your columns are quite 'wall-like'. Spacing not exceeding 3x the lesser dimension (thickness for a wall).

I noticed in 9.6.1 (1) they have defined walls are "walls with a length to thickness ratio of 4 or more". Columns are definitely less than that according to the standard. So I believe the 9.6.2 (3) cannot be applied to columns. And max spacing limit of "3X of the lesser dimension" goes against the my intuition as well.

 

[Pretty Girl7]

Pls look clause 9.5.2 Longitudinal reinforcement for columns

and ,

9.5.3 Transverse reinforcement

(6) Every longitudinal bar or bundle of bars placed in a corner should be held by transverse reinforcement. No bar within a compression zone should be further than 150 mm from a restrained bar.

Thank you. I believe this clause makes more sense of the spacings. But it's strange that they have placed it under the topic of "transverse reinforcement" in the standard. I can see it involves transverse r/f, but it's more about the way of placing the longitudinal reinforcement. It's just strange. May be they are trying to convey more information than just the spacing.

 

[centondollar]

Longitudinal reinforcement in rectangular columns is placed where it's most needed, i.e., close to the edge in the side of the cross-section with tensile strain when bending is applied. Required minimum reinforcement (to prevent brittle failure of lightly-loaded, sometimes non-structural columns) and skin reinforcement (to prevent local spalling and cracking) are an entirely different matter.

 

[Agent666]

Thank you. I believe this clause makes more sense of the spacings. But it's strange that they have placed it under the topic of "transverse reinforcement" in the standard. I can see it involves transverse r/f, but it's more about the way of placing the longitudinal reinforcement. It's just strange. May be they are trying to convey more information than just the spacing.

It's in the transverse reinforcement section in most codes I'm familiar with as it is more about providing a longitudinal bar in the right place for the transverse reinforcement to do its primary role of confinement of the concrete core. It really has little to do with the placement of the longitudinal reinforcement itself for the sake of the longitudinal reinforcement acting under flexure.

Too widely spaced and the core of the concrete section become less confined.

https://engineervsheep.com

 

[CovertShear]

Hope this helps.

img link :

https://imgur.com/a/imSyx4q

 

[Settingsun]

I don't think there is a limit in the eurocode for the most basic columns aside from a bar in each corner or four in a circle. Could be wrong but would expect someone would have pointed to it by now.

Limits might kick in for some cases such as if the column goes into tension due to bending (Centondollar's point), or for confinement when the ties are non-circular (as mentioned by Agent666). Otherwise, it's up to the designer to decide what's reasonable.

I don't think the 150mm maximum distance from unrestrained bar to restrained bar quite answers the question. You could have bars very widely spaced and restrain all of them to satisfy that requirement.

 

[Agent666]

It does seem weird that it implies 300mm max if you have every alternate bar restrained, but provides no guidance if you have all of them restrained.

As far as I can tell ACI has more or less the same ambiguous requirement, which suggests every alternate bar can be restrained provided you satisfy the 150 spacing in each direction. This drives the maximum possible longitudinal reinforcement spacing, but still leaves the ambiguity that if you have a link around each bar how far can the spacing be pushed? I believe the intent is 300 max,

Edit found it in ACI, clause 18.7.5.2 applies where earthquake design is required, picture form that clause noting 350mm, which as drawn would then violate the 150 spacing requirement in clause above.... nothing like inconsistencies in codes....

NZ code has pretty clear requirements for this for when inside or outside potential plastic hinge regions, and I'm surprised EC2 or ACI doesn't have something similar. Clauses below and relevant commentary for your info.

picture to illustrate the requirement

We also still have the same 150mm requirement though interestingly it is only in the beams section of the code which I've never appreciated before. But reading the column requirements these spacing are for the cross links, and you can put bar between and still satisfy the 150 spacing so I guess it did not need to be specifically noted (also you have to restrain every second bar, so if you need more bars it drives more cross links at closer centres).

https://engineervsheep.com

 

[Agent666]

Interesting how in ACI it also notes the hook is not to be more than 135 degrees, so 180 degree hook would not satisfy the requirement. Whereas in NZ code hooks have to be at least 135 degrees. Wonder what ACI has against 180 degree hooks.... Never been keen on the 90 degree hooks in cover concrete, definitely been shown to be inferior.

https://engineervsheep.com

 

[chris3eb]

Agent,

Here are some clarifications on the ACI requirements. You were looking at section 9.7.6.4.4 which is specifically for compression bars in beams. For columns, Chapter 10 provides a few column specific requirements and points you to Chapter 25 for some general requirements. For certain columns resisting seismic loads, there are additional requirements in Chapter 18 as you mentioned. The Chapter 25 requirements are basically the same that you were showing from Chapter 9:

But there is also a figure showing what the maximum angle is referring to. It's not specifying the hook angle, it's specifying the angle between legs of a tie.

The apparent discrepancy between the Chapter 9/25 spacing requirements and the Chapter 18 requirements is because the Chapter 9/25 ones are referring to clear distance and the Chapter 18 ones are referring to center-to-center distance.

Also, here's the section specifying that seismic hooks are a minimum of 135 degrees

 

[Settingsun]

I think a 135-degree included angle is what you get when you run a bar around the perimeter of an octagon.

Straight bar = 180 degree included angle.

Full hook = 0 degree included angle.