Distribution of shear load @ column & shear wall under wind in ETABS

[Samuee]

Hi all,

I recently created an ETABS RC model with 90m high and 10floors (Just for simulation purpose, no design required)

I observed that the perimeter RC column frame account for nearly 0% of total shear from wall, and core wall account for >99.9%.

Are there any mistakes in my model? I expect the column frame will take part some shear distribution with a 90m high structure

I have attached my model here

Thanks

 

[jayrod12]

well 10m9m tall columns will be extremely flexible, so I'd say your analysis output is appearing to be correct. If your columns were gigantic, and there was a significantly deep slab to add any frame action, then maybe. But if your column and slab proportions are somewhat normal, then I would not expect the columns to participate much in the lateral system.

 

[Trenno]

The stiffness of a moment frame consisting of 300x300 RC beams/columns (aka toothpicks) would be so much less than the 8m x 8m 200mm RC box core.

I'm not surprised the core takes all the lateral load...

 

[Samuee]

I have made a more realistic model by changing the floor height 3m, 10floors, total building height = 30m, slab thickness = 300mm and wall and column revised to 1000m x 1000m for simplicity.

However, the result still reveals that the core wall takes nearly all the shear loads... does it indicate that rigidity of the central core wall is really that high such that a 4x4 beam-column frame with 1m x 1m doesnt contribute to lateral rigidity at all?

I attach my updated model here, thanks for your comments

 

[jayrod12]

essentially yes, it is saying that with a rigid diaphragm (300 slab) the majority, if not all of the lateral load will be taken by the core walls. That is due to the stiffness, or lack thereof, of the column-slab moment frames being created. Punch in a bunch of deep stiff beams between those columns and then more of the lateral load will be resisted by the columns.

 

[milkshakelake]

I agree with the other posts. A building like this will have most, if not all, shear taken by the core walls because it's so much more rigid. This particular example has massive shear walls that a real building of this size usually doesn't have.

ETABS comments:
1. Don't put beams and columns where there are shear walls. It adds stiffness. I took them out and now there's a tiny bit of lateral load on columns.
2. Try fixed column supports.
3. Try adding more bays of columns, therefore increasing their overall stiffness.
4. Try adding huge outrigger beams at 10th story. This will make the columns and shear walls work together.

Edit:
5. Don't make a beam that runs all the way across a floor. Try to stop it at each column or wall. It creates analysis errors.