base shear force for building with basement

[luungoclinh]

Hi everybody,
I am designing a shear wall building with 8 storey above ground level, and 2 story underground level. There are 2 cores in the building. The first core finishes at basement level 1, the second core finishes at basement level 2.
My questions is where I should take the value of base shear.
Thanks
Lisu

 

[hokie66]

At the base, which is the lowest level. You also have to deal with the shear at each level above the base.

 

[PicoStruc]

If you are refering to the base shear for seicmic calculation, You are probably refering to the base shear of the ground floor (1 story) where the plastic hinge is deemed to occur.

IMPORTANT : Shear amplification and reversal can and probably will occur at basement levels. (Stayback effect)

 

[luungoclinh]

thanks guys for the responses. I do refer to seismic design here. My problem is because 2 cores in my building dont finish at the same level (one finishes at basement level 1, while the other finishes at basement level 2). One more thing is that I am going to prove appropriate detailing to laterally separate the core from the foundation walls, so I dont need to worry abt backstay effect.

 

[structSU10]

If the basement is 'laterally seperated' from the foundation walls, the bas level is the sub basement level 2. a shear collector will need to be designed to bring the load from the one stopping a level high over to the other. If you have a full height basement, you can take the height of the building from grade level, depending on the situation. The following link brings you to a paper on the subject:

http://www.structuremag.org/article.aspx?articleID=993

 

[luungoclinh]

thanks, the article is very useful

 

[asixth]

Is the basement split level or benched? Depending on the size of the cores the shear will be taken out at both basement level 1 and 2 depending on the foundations of the cores. I had a similar one to this once and the core finishing at the higher level was taking out more of the shear just because of the increased stiffness (smaller cantilever length)