Positioning RC Column 1

[strawhats2000]

Hi,

A question of positioning Columns. Should it be at all wall intersection or should it follow a more rigorous grid line pattern with more or less same X and Y spacing between them?

Thanks.

 

[ShawThing]

Can you provide any additional information and be a bit more specific?

 

[Lomarandil]

Columns are not required at all wall intersections (though they may be useful there).

Your design and design time will be more efficient as you use a more regular grid. Of course, sometimes building use constraints and architects will interfere with that.

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The name is a long story -- just call me Lo.

 

[BAretired]

It is desirable to maintain equal or nearly equal spacing for all columns. Unfortunately, the architect may have other ideas. Sometimes, considerable structural wizardry is needed to satisfy his requirements.

BA

 

[strawhats2000]

Hi.

Here is a sample foundation and architectural layouts. I believe there are more columns than needed. However those are skinny 150x150 columns reinforced with 4T12 (+R6 links at 125mm). Please advise where I can remove columns. I believe a problem that may arise with a grid positioning of columns are that we may have a lots of suspended beams within different rooms. Some clients may opt for false ceiling, others for upstand beams which cause other problems for upper floors or water ponding. Recently a client requested that I inverted the beam. He called it a sleeping beam. Instead of a 425 (height including thickness of slab) x 150, we have a 150 x 425 beam inside the slab, hence with a 150mm. thick slab, the beam is not at all visible. Is that a good solution as also we do have like 6T12 in a sleeping beam instead of 4 to 5 T12 in a regular beam.

Thanks.

 

[Lomarandil]

You need to find a structural engineer. None of us can tell you which (if any) columns can be removed without much more information.

Note that with 150x150 columns, you will find it nearly impossible to develop your beam reinforcing bars correctly.

Regarding the sleeping beam (which I understand to be 150mm deep and 425mm wide) -- this will be significantly less efficient and significantly less stiff than a suspended beam or an upstand beam. You will need much more steel (not only 1 or 2 bars), and the slab will deflect much more, potentially cracking. It is not a good option.

Again, you need an experienced structural engineer, either that you hire to answer these questions for you, or to mentor you through the process.

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The name is a long story -- just call me Lo.

 

[BAretired]

I don't remember ever seeing a column as small as 150 x 150mm. There was a time when the Canadian code required 250 x 250mm minimum column size but that requirement appears to have been dropped in more recent codes. Placement of steel is likely to be a problem as noted by Lo.

BA

 

[MIStructE_IRE]

I’ve never done a 150mm wide column.. I can’t see how it meets any fire requirements let alone detailing/bending bars into something so small.

 

[strawhats2000]

Hi MIStructE_IRE,

I know that 150 mm x 150 mm is out of norm with official code we are supposed to follow but most houses here is made of this size of column and sometimes we do have span exceeding 4.5 m and even G+2 house on such skinny support. This is a basic issue and I don't think we need to study years of engineering to tell us what is the minimum size for a RC Column but it seems so to many people, even on this forum. I asked like a question on guidelines/codes/books regarding position of column and the answer is again go look for an engineer. Engineers here are building G+1 house, 4.5m span with 150x150 column reinforced with 4T12 on 900x900 Pad Footing.

So far I believe columns should be based on a grid system, more or less, based on standard room size, nearest to corners of building and room as suspended beams are considered an eye-sore for many. For wall intersection, I believe we can have what we call "Tie Column" or Block infilled with Concrete and Reinforced centrally with 1T10. The Tie Column is a Column without Pad Footing but can be rooted to the Strip Footing below or simply to the floor.

The 150x150 Column is much of a problem. Some tries to solve it by a 150x200 Column but still I believe that the min. size for a column should be 300x300 but on a practical stand, we have much to go.

Thanks.