Shear wall Discontinuity

[AniMhj]

Dear everyone,
I am modelling a building for banking purposes. It has vault at the ground floor and parking at basement.
The vault has shear wall which cannot be continued to the raft foundation as it disturbs parking area in the basement.
I cannot see the effect of this discontinuity in ETABS model.
How can I address this effect by manual calculation?

 

[JLNJ]

How does the shear get to the raft if you have no shear walls? Do you have a load path? What is Etabs telling you?

If you are in a high-seismic area, such a discontinuity may not be permitted (or at least be severely penalized). What is your seismic design category and what is your governing code?

 

[AniMhj]

Dear JLNJ,
I also have the same doubt regarding the transfer of forces due to the discontinuity of shear walls.
As much of the forces in the basement are taken by the basement walls which run the along the periphery of the building, these vault shear walls carry less load when modelled to the base.
According to the code (Nepal National Code), these discontuity is treated under vertical irregularity and the code says the effort shall be made to make structure as regular as possible. So, there is no clear provision on how to deal these cases.

 

[JLNJ]

Maybe you need a different lateral force resisting system.

 

[cliff234]

Is the lateral load going into the basement walls? Doesn't the model show where the base shear are at the foundation level?

 

[hardbutmild]

Could you provide a drawing? It is hard to follow what's happening without it, especially since we each use a different name for the same thing. I'm confused by the term "vault shear walls", first time hearing that.

 

[AniMhj]

These vault walls are the RC walls of thickness 450 mm. These walls are provided for security reasons as per client requirement. The problem is that these walls cannot be extended to the basement or raft foundation as it will disturb the parking area.

 

[hardbutmild]

What makes it a "vault" wall? Is it supported on a vaulted shell? Is this wall curved like a shell?

 

[phamENG]

banking purposes

I'd say it means it holds the gold and jewels.

 

[hardbutmild]

ahhh... ok, it's the wall of a vault. I somehow did not register that, it didn't even cross my mind.
You should see the shear force go from that wall to other stiff walls of the basement. If the perimeter walls go down to the basement, they should have a larger increase in the shear force.
By hand I'd calculate the stiffness of all the walls in a basement sotrey and divide the total shear force in accordance with their stiffness (stiffer wall takes a larger force), do not forget the torsional effect. You can do the same thing for the ground floor. That way you should be able to see that there is a force in the vault wall and that it gets transferred. You also need to check if the diaphragm can transfer that force.

Since you're in Nepal I expect high seismicity so it's a bit more complicated. Do you have some walls that are continuous from the bottom to the top (or near the top)?

 

[AniMhj]

Thanks for all the replies.
Most of the shear walls of vault are only at the ground floor. There is only two walls that go to the top. I think I will have to continue these walls to the raft.