AS3600 Section 14, height limits on walls

[rscassar]

Good afternoon,

I have a wall in a building where structural ductility of 2 has been adopted. There are limits to the aspect ratio and slenderness of walls when using mu=2. I have got a scenario where I have a structural wall where there is no other option but to exceed the height-thickness ratio of 20 as prescribed in 14.6.5. Because I have no way around this, I am going to design this wall as "non-ductile". Is it acceptable to design an element as non-ductile (design for forces for mu=1 and also provide the detailing for limited ductile walls) for an isolated element in a building where mu=2 has been adopted.

 

[Gishin1]

Hi rscassar

Some will tell you that the paragraph under table 14.3 is the answer - the least ductile element in the combined system governs the whole system.

However I feel this is more applicable for a building that has say a full-height core box and a full height shear wall/moment frame. The combined system is comprised of the dominant lateral stiffness elements.

If you have a single level wall somewhere in the system, it shouldn't be attracting much lateral load anyways, given its size and position, so I think it's rational to design it as non-ductile, if it behaves in a non ductile manor under Mu&Sp of 1&1.

It's essentially the same as a wall that has a permanent slip joint from the floor diaphragm to ensure it doesn't attract lateral load, except the slip joint is achieved by the wall's low relative stiffness compared to other elements in the system.

Of course, this is all on a case by case basis.

 

[rapt]

If everything else at that level is designed for mu = 2, then that wall has to be also.

 

[rscassar]

Looks like I'm back to mu=1

 

[Trenno]

Out of curiosity - what is the situation? A rear wall of a lift shaft with a massive riser adjacent?

 

[Retrograde]

A rear wall of a lift shaft with a massive riser adjacent?

That probably would not be an issue as the effective height will be limited due to the lateral support of the return walls as per Clause 11.4.

 

[Trenno]

Very true...

 

[rscassar]

Retaining wall which exceeds 20 to 1. I can't disengage it from the building, Don't want to thicken it but probably will to get the 20 to 1 ratio cause only need 50mm to get back under the limit. Was a precast wall which is segmented. Stitching it together to go to a squat wall which can be designed using mu=1

 

[li0ngalahad]

If the connected slab and footings are stiff enough to rotationally restrain the wall, and you detail the conenction accordingly, you can reduce the effective height of the wall by a factor of 0.75 and hopefully be below the 20:1 requirement

If not, I see nothing wrong to design it as non ductile, even if you don't stitch it togehter - as long as you have the un-reduced seismic load in you combination - i.e. you are sure the other walls detailed for ductility will develop plastic hinges while this wall will remain elastic. Probably in this case I'd use the mu=1 Sp=1 load, not just mu=1.