Buckling of Very slender wall - elevator wall / exterior staircase wall

[structural87]

Hello
Whenever u have a very slender reinforced concrete wall rising many floors without any lateral bracing (core elevator for example - H shape having its web braced at the ends but nothing in the middle and the web is quite large in plan), how do u treat such element versus buckling ?
Another example is an exterior stair wall braced at every floor from one end, and by a small landing at the other? Do u consider that the landing offers a stiffness which prevents the wall from buckling in its out of plane ?
I generally try to limit the compressive stress as low as I can but I.cant find any reference in the literature which deals with such elements.

Thanks

 

[WARose]

For a elevator shaft, I typically take the effective height as being a 1:1 aspect ratio for allowable compressive stresses. In other words, if you have a wall width of 10'.....the effective height for calculations will be 10'.

 

[structural87]

Any reference Warose for the above ?

 

[WARose]

Any reference Warose for the above ?

None I am aware of. (Except engineering judgement.) That check would eliminate a localized buckling of the shaft. So what would control over that (as far as buckling goes)? The shaft as a whole? Not likely, unless we are talking one tall shaft.

 

[structural87]

I agree. How about an exterior stair case wall braced from one end and from the other hand by a small element like a landing ?

 

[WARose]

Hard to say without a pic.

 

[structural87]

Hello

I attached my case. I am sure lot of people have faces this problem. The problem is that how to assess and quantify how much stiffness does this landing offer in order to be qualified as a bracing. And how to treat such element versus buckling ?
Thanks

 

[WARose]

Something like that would kind of be like the elevator shaft: braced at the ends.....so it would become a aspect ratio deal. You'd have to check that the out-of-plane stiffness of that wall so that the landing "brace" between floors is stiff enough to act as a brace for that end of the wall.

And all this is presupposing that wall perpendicular to the shaft is a shear wall stiff enough to provide adequate bracing as well.

 

[structural87]

Yes I do agree. But the question is how to quantify it ? On which basis do u found to.say that this is stiff enough?

 

[WARose]

I typically fall back on the bracing seminars I've attended (by Yura) or the AISC specification (i.e. Appendix 6). All that has the required stiffness for bracing.

Granted it's for steel, but if you are considering the correct form of buckling.....it should be ok. (ACI has always been a little vague on this IMHO.)

 

[Guest262653]

Table 12.6 in Eurocode 2 Part 1-1 (unreinforced elements section) defines the buckling length factors for walls. We use it for reinforced walls as well.
I enclose a pdf with the transcription of section 12.6.5.1.

The full code can be obtained for free with a simple google search for 'eurocode 2'.

 

[structural87]

What if the slab edge A isnt located along the.total edge length and is at 50%from.the length of the wall ? What is the effective length factor in this case