Transition between column and shear wall 1

[IJR]

In my area a shear wall is defined as a vertical element with planar aspect ratio of 7 and above, ie depth to thickness ratio of 7 with depth here in analogy to depth of a cantilever beam.

Why 7 and what is the +/- margin?. What will happen if I design a column with aspect ratio 6.67 as a shear wall?

respects
IJr

 

[JAE]

Not sure of the source of your "7" limit, but perhaps the limit is to ensure that your shearwall will not buckle. When the wall receives lateral force, it cantilevers out of the floor and experiences lateral shear across its face and vertical stresses due to bending.

Perhaps the compressive side of the wall (at the wall end) will possibly create a potential for lateral buckling, and thus, there is a limit as to how thin you can go.

 

[ishvaaag]

The question is even compounded in the label being misguiding, for many or at least some of the called shearwalls in tall buildings are thought to work mainly in flexural ways. What does not mean that ir modeled as columns the shear can be dismissed for interstory heights. A shear-shear wall should be so squat as to act mainly in shear, no? Maybe then we would be having only shearwalls in low buildings.

 

[phuduhudu]

You should be able to design a column with an aspect ratio of 7 as either a wall or column. E.g a column 7m high and 1m wide could be either. However normally columns are restrained at each story height but shear walls of course cantilever from the ground. Also as JAE points out with a very tall and very wide column you should watch the depth/width limit to avoid lateral buckling unless there are also cross walls (E.g. in a lift shaft). The concrete and reinforcement doesn't know whether it is in a wall or a column. It only sees a set of stresses it is exposed to. This is where the designers skill comes in - in using the best model.
Carl Bauer

http://www.bauerconsultbotswana.com

 

[ishvaaag]

I think we are having mixed things here. On the one hand I understand 1st entry express it is in section that the shape must be 7 to 1 to be thought as shearwall.

On the other hand, the same first entry refers to cantilever action, as does Carl in the previous one, like if saying if it has such overall in the plane of bending height to depth ratio should be as stiff as to ensure that the way of functioning is that of something fixed at the base, cantilever action, then not exactly mostly shear action, but taken as the common ordinary behaviour of shearwalls, where "cantilever" action of the stiff shearwall far exceeds any frame action of the accompanying columns and beams, in spite of its behaviour be not only mainly through shear deformation, but also and even more in bending.

Last time I heard of this thing in print here was reading something on structures against wind of the sixties or so, and referred to the in section proportion. It is only natural that shearwalls, that must rule the lateral displacement behaviour neeed be stiff, and those such rule of thumb specifying were not thinking in gross columns. Then we have been having cores and many other kinds of structural systems (tube in tube etc)

So you model your thing in whatever way it is suitable to your structure, and ensure whatever compliance required by the code is met; I wouldn't give further thought to this.

 

The question whether a "column" becomes a "wall" for design
purposes (specially when you mean shear wall to be designed
as flexure member) is a good one and leads to many interpretations.
But for design purposes it's very clear in ACI 14.4.
It has to be designed as "column" for vertical reinforcement
and later designed for shear in compresion members.
That's why some books use "PCA Column" program to design shear walls.