Concrete Frame - Rectangular Perimeter Columns - Pros and Cons 1

[liam1369]

Good Afternoon All,

I am scheming a concrete frame for a education building over a basement. It is only 4 stories and will be 'braced' with concrete cores and walls, therefore, all the columns are to be considered as 'braced.

As part of the proposal, I am proposing to make the columns rectangular to better fit in wall lines and not stick out in large classrooms etc. However, does anyone have any experience with these rectangular columns. In particular the following:

- Dimensions: At present I am thinking of going for 250 wide by 500mm long columns, to help with fire and give an initial section size. What is a typical size for a 4-5 story building with column grids circa 6x7m with flat slab 250-275mm.
- Orientation: I am initially thinking to have the longer side (500mm) of the column to the external perimeter line, this will help with moment and anchorage? - I know it is about the weaker axis though, however, I don't think there will be too much issue.
- I have proposed a 100mm - 150mm perimeter edging / nib which helps out with infill walling or build up required. Potential air gap cavity before masonry support angle springing off of the edge.

I have attached a couple of JPEG images clarifying what I am proposing above.

Does anyone have any experience with concrete frames and design of columns / flat slabs in general? Is there a benefit to orientating the columns so the longer side aligns with the slab perimeter edge or is it better to rotate so the shorter axis aligns to the perimeter edge?

Looking for initial pros and cons or whether there is a better way of doing things. I do not have much experience with concrete frames.

Many thanks for any help or input into this, I will be interested to know your thoughts.

Kind regards,

Liam

 

[ThorenO2]

@liam1369, since you'd indicated you do not have much experience with "concrete frames", it sounds like an opportunity to steer the project towards larger columns that stick out into the classrooms and do not fit in wall lines. Secondly, I'd say you really shouldn't approach the design using the word "only" as in "only 4 stories". It actually sounds like a massive building requiring the utmost engineering and a whole lot of safety factor. "Only" is pretty much reserved for 1 story buildings only. Best of luck,

 

[dik]

I'd generally run the columns with the wide dimension parallel to the edge. They attract less moment and less of an issue with punching shear. They are also less obtrusive in wall systems. Moment transfer is not an issue since it is not a really tall building and you have 'rigid' stair wells and elevator shaft.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[liam1369]

Thanks very much Dik. Your comments are very helpful.

 

[HTURKAK]

Flat slab bldg with 6x7m circa and thk 275mm will create substantial load for punching and 250 X 500 mm columns seems small..

I would go ,

- I would decide the column size acc. to punching check and would prefer column size 500X500 or at least min dim. 350 mm for fire resistance,
- Provide perimeter dropped beam ( spandrel beam having similar width of exterior masonry wall ),

 

[liam1369]

Hi Hturkak,

Punching shear is working ok as the columns all stack and with 275mm slab is working ok.

500 x 500 is quite large, I don't think I can use that.

Equally for the perimeter beam, it is a glazed curtain walling so will be looking at options to avoid beams.

Kind regards,

Liam