Changing Column Size 3

[dr. rifat]

Dear engineer,

I have a query about column design.We designed a 11 storied building.Which a column size is 12''x 36''.Which As=13.2 in²-3.05%.
But my project engineer argue this size,he suggested me to keep column size 15''x 36'' for workmanship.Also from architectural point of view we have to limit it 36''.So we cant decrease the size.Now my question is if we increase column area,is it need to increase steel area? or we can keep it same.If we keep it same As=2.44%.If we increase steel area it is uneconomical.What is your suggestion please??

RIFAT

 

[jayrod12]

It would depend on what you need structurally, I agree that a 15" wide column will be significantly easier for the guys on site. In terms of reinforcing, as long as you are meeting the minimum required by code or by structural analysis and not exceeding the maximum allowable reinforcing, then I don't see how it would be a problem.

 

[kipfoot]

My suggestion: keep the same reinforcing for the larger column size and use ties that take advantage of the additional 3" width.

 

[dik]

The larger column size may be more economical...I don't know, but the larger column size takes up more floor space which may be an issue and there is an economy to be realised.

What are the column sizes above and below?

I assume this is a perimeter column.

Dik

 

[dr. rifat]

jayrod12:Your suggestion is we can use same reinforcement in larger column??Our code limit is 1%-8% and smaller column have 3.05% if we increase it would be 2.44%.

kipfoot:Thank you for your brilliant suggestion.That means same arrangement,same ties is your suggestion?

dik:Yes brother it is perimeter column.

RIFAT

 

[KootK]

Our code limit is 1%-8% and smaller column have 3.05% if we increase it would be 2.44%.

Sounds as though you ought to be fine. In addition to being over 1%. you'll want to ensure that the reinforcement that you do have is distributed in such a way that you still have the moment capacity that you need. That would be pretty hard to screw up, however, if this is a perimeter column with it's long side parallel to the slab edge. Usually, making flexural things deeper has a positive effect. Of course, it also means that your column will also attract more moment than it would have when it was smaller.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[kipfoot]

That means same arrangement,same ties is your suggestion?

I meant to suggest that you use a bigger ties for the bigger column. In other words, if you had a tie that was 10" x 34" change it to be a 13" x 34".

 

[dr. rifat]

Of course, it also means that your column will also attract more moment than it would have when it was smaller.

Thats why I cant decide,whats your suggestion?If I increase the size or not?

RIFAT

 

[dik]

OP:

Try both approaches, and see what works best. When doing long span beams for parkades, it was often best to have the columns with minimum depth to minimise the moment...

Dik

 

[KootK]

Thats why I cant decide,whats your suggestion?If I increase the size or not?

I'd go for the size increase and then either:

1) check it for the new moments OR;

2) don't check it if you're able to confidently use your judgment to assess the outcome.

Seeing as you're here asking this question, I suspect that #1 is the right path for you. That, or let your supervisor make the call.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[hokie66]

I agree with your "project engineer". Constructability is very important in high rise construction, and 12" columns can be a problem with compaction.