Multistory concrete frame - shear wall stiffness vs unrealistically high reaction.

[lawrence_budzisz]

Hello Everyone, 

I was wondering if someone here know how I could overcome an issue. I have modeled a multistory concrete frame building with concrete walls and acting as shear walls. I understand that FE results are going to be slightly different than hand calculation but when conducting a load take down check the reaction from the shear wall support are 3 times greater then what I anticipated. Obviously this also means that some of the columns do not pick up as much load as they should. I understand that the walls are much stiffer and will attract higher loads however my results appear to be excessively high. Any ideas how this could be resolved?

Looking forward to any assistance on the matter, 

[Simau]

@lawrence_budzisz 

It would be helpfuf if you share your model.
zip it before attaching

[lawrence_budzisz]

Hi @Simau,

Thanks for getting back to me so fast. I had some issues to upload the file as it is 110 MB but managed to compress it down. 

You will see that the shear walls are modelled between columns and supports are defined at the bottom of the columns. the columns in the shear walls attract a significantly larger portion of the force. 

Kind Regards,

Lawrence 

[Simau]

@lawrence_budzisz 

Your shear walls have no linear supports.

When adding supports walls reactions are almost similar in LTD and FE models

[lawrence_budzisz]

Hi @Simau ,

Thanks a million for the explanation. I was hoping there is a way to collect reactions without having to model linear supports. Is there a quick way to change the analysis type from FE to the Load Take Down (LTD) option?

Kind Regards,  

[Simau]

@lawrence_budzisz 

You are welcome

Select all your floors then

[lawrence_budzisz]

Hi @Simau ,

Thanks for that. I conducted further checks and found that the results still do not match the hand calculations. I even extracted a core slice from the model, and in isolation, it matched the hand calculations. However, when looking at the main model, the shear walls attract 50% more load. The total model reactions are correct and the issue lies in shear wall locations attracting more load than they should.

I have included some photographs. Any idea why the model would behave like this?

1 - Effective region for LTD check - central shear wall 

 

2 - Extracted Core and analysis 

3 -  Main model shear wall comparison

 

Kind Regards,

[Simau]

Hi @lawrence_budzisz 

I made some modifications to your original model and modelized 2 models (FE & LTD)

- I deleted columns nested into walls

- I merged the first floor walls

- LL load case is 1kN/m²

For the wall 2232 we get

[Simau]

Models attached

https://we.tl/t-rvD0EUY64A