What should we consider in design and detail of tapered RC columns 2

[IJR]

My valuable friends

Is there anyone here who wants to share his/her knowledge on performance and design of tapered reinforced concrete columns.

I notice many friends including myself taking this element almost for granted: take the narrow end as effective column and add some minimum requirements along the taper towards the wide end.

Makes me uncomfortable designing something I have no good control of.

Thanks in advance

 

[dik]

I've not been involved with tapered columns in a while and those were not what you would consider as being very slender. They were designed as regular columns at the small end as you noted. Because there were not many of them, I supplemented the ties with additional ties to carry the horizontal component of the skewed rebar loading. No rocket science.

I've not done one where slenderness was the issue, but I tend to design columns quite conservatively considering the consequences of redistribution of the forces <G>.

 

[JAE]

IJR,

If you're modelling this in a program, you should probably adjust the stiffness and area along the length to allow the analysis to include that effect. You could do this by adding multiple nodes along the length of the column.

You can deal with each &quot;section&quot;, its properties and loads along the length and design accordinly.

I remember reading about Frank Lloyd Wright and his design for the Johnson-Johnson building some years ago. He had developed a weird, tapered and flared column that looked like the stem of a wine glass turned upside-down. The building department wouldn't accept it as they thought it wasn't strong enough. (it was quite skinny at the bottom).

He built one and load tested it to a much higher load than required. There was a famous picture of the column with a dozen or so men sitting on top of a huge pile of sand bags on top of this thin concrete column.

But be conservative anyway.......