ETABS Column reactions vs Column Load Take Down

[matrixeric]

Hello All:

I am modelling a 10 story concrete 2-way slab/concrete columns/concrete shear wall model in ETABS. I have defined the concrete 2-way slab as a shell.
Now coming to the problem, the reactions I obtain at columns are <50% of what I obtained from column (made sure that column is far from the core) load take down for couple of columns.
I have tried checking every possible cause for error but haven't found any logical explaination of why this is happening?

Any help will be greatly appreciated !!!

 

[inju]

Hi,

As I understand the situation it seems like the load from the shell is not distributed to the beams (columns) in a two-way fashion. I would suggest that you mesh the shell element after you assigned the surface loads (self wt, live load, snow load .. or whatever)
If you are using ETABS version 9.0.8, try ASSIGN>FRAME/LINE>AUTOMATIC FRAME SUBDIVIDE
ASSIGN>AREA/SHELL>AUTO MESH
(make sure to keep a temporary back-up of the file before meshing)

 

[Murali27]

Hi matrixeric

I would suggest to go ahead with inju's suggestion if we are aiming for realistic distribution. Especially it happens for corner/edge columns, where force will be very less compared to manual trib area calculations.

If we want to match with manual method, please go ahead with membrane option and connect the beams (null) on each vertical element. It matches with manual calculation.

Please also check with Tributary area for each column in the ETABS output.

Cheers