Footing column ties

[mes7a]

Do you put column ties inside the footing? What is the failure mode if no such ties were put. The column can't dilate outward inside the footing itself because it's surrounded by concrete.. or can it? I don't see this mentioned in references..

 

[KootK]

I don't see a need for such ties. ACI requires them at the edge of footings in some seismic zones I believe. But that's s substantially different situation.

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]

Ties inside the footing serve little structural purpose, but they do assist in constructability by supporting the column dowels. What you seem to show is a full height column cage, and the column cast monolithically with the footing. That is not a practical way of building a column.

 

[Trenno]

Helps to hold the column starters in their correct position whilst pouring the footing.

 

[JAE]

Trenno - that is a possibility but you'd only need one at the bottom - and in most cases we try to simply tie the bottom hooks to the footing bottom bars so ties are not needed for bar positioning stability.

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[mes7a]

This is file record pictures of what our contractor did two years ago.

They don't use dowels.. but directly planting the 14 meter rebars (16 to 20 pcs of 20mm size) into the 0.6 meter thick foundation. What they do is tie all the rebars at the middle and upper part together against the neighbor walls for support.
In the picture above.. initially there are no ties inside the columns within the foundation. But later I told them to tie them up after formworks done. See picture:

There are top rebars in the footing because it is a combined footing that has 3 columns in a row.
I'd like to know if the connections details of the foundation above is adequate to create fully fixed column bases and foundation. How much moment (approximate in percentage) before the column become pinned or rotates)? Or would it only become pinned at probable moment strength of the rebars at the base?

The soil is very stiff soil and the foundation were 3 times normal size for strength. Fully fixed is done to ensure less possibiity of soft storey since the ground floor is 3.5 height and second floor is 3.2 meters height. The rebars from foundation to third floor roof is not spliced but use continuous 14 meters bars.

 

[mes7a]

It's true but many designers I know have the column ties underneath the footing. I'm asking all this because when I got the contractor to tie it up. They had difficulty turning the ends property.. one part where they just inserted J crosstie bar instead of hoops. Now with additional load in the roof. I was worried the bars may dilate outward.. but I realized the footing has enough concrete to prevent the ties from opening. But now thanks to you I found out the ties are not even necessary.

 

[mes7a]

taken from actual structural plan:

taken from actual structural plan:

To continue.. here's the weird part. Most structural plans I see have the column ties below footing.. such as the above 2 from actual structural plans. Is there a possibility that in full length column cage with the column cast monolithically with the footing. It has function like during rotations of the connections? Just mentioning in case someone sees a reference about this somewhere.. I forgot where I read this (this is the reason I was a bit concerned because I added some weight in the roof with hoops not completely used but crossties inside the foundation column ties.