Is this 350mm long wall to short? 2

[UpsideDown]

Due to the architectural layout, there are many short walls (150mm thick, around 350mm long, precast) on the external, between these short walls are floor-to-ceiling curtain walls/doors so no beams are used, just flat slab on top.
I have run the analysis and the results are fine including punching shear (Max. design axial force are around 100kN) However, I feel like these precast walls are too short and there might be some potential structural issue that I miss?
Below is the part plan & 3D view.

 

[UpsideDown]

 

[CANPRO]

You’re talking about those columns right?

 

[r13]

My feeling is the short panels are too thin. I would increase the thickness to 200mm-300mm to better resist the anticipated torsional stress, and deflection.

 

[dik]

Depending on the height, they may have to be designed as columns.


Dik

 

[UpsideDown]

They are precast walls. Shown in red in the pic.

 

[UpsideDown]

But isn't 150mm thick wall quite normal? I have checked the P-D and they are okay too. Everything looks fine from the comps. I just haven't used walls with such short length. But I cannot tell what is wrong as well.

 

[UpsideDown]

The height is 3 meters. What are the potential issues if I design them as walls?

 

[Retrograde]

But isn't 150mm thick wall quite normal?

Not if the wall is only 350mm long. Have you checked the fire rating?

 

[UpsideDown]

Yes. I have checked fire rating using Tedds (as wall) and it pass. That's why I got confused. So how long is adequate and why? I just have this feeling that it is too short but I cannot explain.

 

[Settingsun]

Are you wondering why you could take a smallish column, halve the cross-section, and then get reduced reinforcement requirements as a bonus?

 

[Phil1934]

Search Opal Tower in Engineering Failures for debate on col. vs. wall

 

[Trenno]

You'll only be able to get 3 or 4 bars into a 150x350 element - not great from a robustness perspective, a lot of codes are shifting engineers away from detailing vertical structure with single layers of rebar.

I would increase the thickness to 200mm, so you can get two layers of rebar (say 6B16 bars) and tie it all together with an outer link loop (say B10 bars). You then have a 200x350 column. Check strength capacity and fire resistance as a column not a wall.

 

[JLNJ]

What is your lateral force resisting system?

Is this the whole structure or is this a piece of a bigger building?

 

[dik]

You may not have an option about designing them as columns.


Dik

 

[UpsideDown]

So, if I design them as wall, for 150mm thick what is the min. length I can use and where I can find the clauses for this (I am using AS3600)?
If I design them as column (say 200mm wide) what is the min. depth, does the code cover the min. depth for column?
I only find that there are requirements for the width (weak axis) for fire rating, no luck with length so far.

 

[UpsideDown]

Sorry steveh49, I don't quite get your question.

I have a core wall on left hand side, this is just part plan.

 

[UpsideDown]

I don't think 200mm will pass for fire check if they are designed as column, might try 250 if I make them column. I will probably keep it 150 or increase to 200 but design as wall and increase the length instead if I can. Don't know the min. length required though.

 

[Trenno]

These elements, with the 1:2.33 proportion you've stated, are definitely columns. Wall code clauses do not apply.

These elements would need to be atleast 600mm long to be considered as walls, using a 1:4 aspect ratio. Even then, 150mm thickness and single layer rebar isn't a great idea.

I know AS3600 had some recent updates that heavily discourage single layers of rebar in vertical elements. Take a look for relevant threads here: [URL unfurl="true"]https://www.eng-tips.com/threadminder.cfm?pid=744[/url]

 

[UpsideDown]

Thanks Trenno, Where does AS3600 cover this 1:4 aspect ratio?
Do you mean not single layer is not recommended for all walls (which means all wall thickness should be greater than 150mm?) or just not for single layer for short walls? Because if it is the former, I have seen too many plans with single layered 150mm walls. I will check the updates of AS3600. Thanks