Reinf Spacing limits for concrete column/pier

[BurgoEng]

I understand that longitudinal bars but be within 6" of a corner of a tie. However, is there a limitation on the maximum allowed spacing of the longitudinal bars, regardless of corners? I had always thought it was 12", but I can't find the reference for this.

Example, 10" x 20" col. I want to use 4 bars and As(min)=0.01Ag = 2.0si. I choose 4 #7 = As=2.4si. Can I put the 4 bars in the corners with 1 tie? Along the long side of the col, the bars will be about 14". Each bar will be at a corner, which is good, but what about a max spacing requirement?

 

[JAE]

ACI 318, section 10.9.2 is it.....your 4 bars are fine...just be sure you have 1% min. steel. The rest is your own engineering judgement.

 

[youngstructural]

Just to put in my two cents...

The New Zealand 3101 Concrete code is basically the ACI 318 with a great deal of improvement for seismic construction. It's basically the only load case that matters for concrete (a gross exageration, but one with some truth to it). The most recent code has just made 8 longitudinal bars the minimum for columns... Something to think about anyways.

Cheers,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[JAE]

youngstructural - good point. For US use - in ACI 318, I don't know if the seismic chapter suggests anything similar to the 8 bars. I'll have to check tomorrow at the office.

 

[WillisV]

True, there is no maximum limit for the main vert. reinforcing bars in column. However I believe it is prudent to at least maintain a reasonable (say 18")limit for temperature and shrinkage type reinforcing in large columns. For instance if you had a 20"x48" column you could technically make that work with 4 No. 11s (using the reduced section for design it is allowed to go down to 0.5% reinf). I would be hesitant in using just 4 bars in this case because leaving such large expanses of concrete unreinforced could have negative effects regarding shrinkage and creep...

 

[dik]

The larger number of smaller bars will help with ductility; shrinkage may not be an issue with most columns...

Dik

 

[BurgoEng]

Thanks gang. Maybe it was just a rule of thumb I had picked up along the way to keep bars within 12" of each other. I was going nuts trying to find the "fact" somewhere.

 

[xxpegasus11]

I can only comment on the UK code - I imagine US codes would have something similar. For Column compression reinforcement the requirement is for every corner bar and each alternate bar in an outer layer of reinforcement to be supported by a link(tie) passing round the bar and having an included angle of not more than 135 degree. It further stipulates that no bar within a compression zone should be more than 150mm from a restrained bar. Perhaps this is what you are referring to. If one had an intermediate bar for instance, the maximum distance would be 6" from the corner bar. If, however, you only had corner bars, then the corner bars are themselves individually restrained anyway, so the 6" distance wouldnt apply.