Gravity Support of PT Concrete Slab @ Shaft

[KootK]

I'm working on a post tensioned concrete building with concrete shaft shear walls. The column spacing is pretty regular throughout.

At two locations, however, there are concrete stair/elevator shafts that essentially take the place of columns (i.e. there is a shaft wall where a column would have landed in the absence of the shaft).

Based on my judgment and the advice of my peers, I intend to treat the shaft wall as gravity support for the adjascent slab. Essentially it will be a big, funny shaped column for gravity purposes.

I have the following questions regarding this arrangement:

1) Does it seem reasonable to use the shaft walls in this way?

2) For modelling purposes, should I assume that the column is located at the centroid of the shaft wall section? This is complicated somewhat by the fact that my shear walls are C & L shaped sections.

3) Are there any special detailing concerns that I should be aware of?

Thanks,

Adam

 

[AlohaBob]

You may wish to consider the shaft in the center of an isolated prestress sequence to minimize shrinkage effects. The shaft walls are likely very stiff in comparison to the columns. So shrinkage deformations would be more evenly distributed at the perimeter of that sequence.

 

[structurebeton]

Adam,
What kind of software are you using to calculate your post-tensioned members?
Only beams and columns are posttensioned, correct?

Do you have a good reference for the design of post-tensioned buildings?

And, finally, do you think construction cost is much cheaper than regular reinforced concrete or even steel?