RC Shear Wall Load Division 1

[otto_eng]

Hi Folks,

This is rather a theoretical question for the experienced structural engineers. How do you guys assume the shear wall load transfer and the bending moment reinforcement consideration at the ends of a shear wall when only a portion of the wall is directly sitting on the foundation wall below ? The rest of the wall is sitting on a RC beam in some situations and in others it is directly on the ground floor slab so acting as a deep beam. You can consider half of the wall sitting directly on a foundation wall and the other half on a RC beam or ground floor slab. Also as a note the entire length of the wall is connected to the diaphragm/slab.
I would simply design the part that is bearing on the foundation wall as the shear wall and also consider the stiffness of that portion of the wall for the lateral load distribution even though the entire wall is actually not seperated. I would like to get some opinions about this. Has anyone of you encountered with such a condition ?

Thanks!

 

[HTURKAK]

İt is not reasonable to assume half of the wall sitting on the foundation wall and the other half on ground floor slab or on RC beam.

My suggestion is , model the base slab ( i think inverted bowl mat found ) with plate bending elements supported on Winkler springs and model the walls FEM plane stress element supported on the raft and /or beams.

You may post a detailed sketch to get better responds.



Use it up, wear it out;
Make it do, or do without.

NEW ENGLAND MAXIM

 

[milkshakelake]

I don't think you can just take the portion of shear wall only sitting a solid element, like a foundation wall. In reality, the wall will act monolithically. This will add some tension and compression into the supporting beam or slab. I wouldn't worry about horizontal shear too much, because generally that will mostly go through the foundation wall and the supporting element will act as a collector.

The stiffness of an element below a shear wall is related to how much shear that wall will attract. If you separate the single wall into two shear walls, it's not accounting for this effect. I personally can't do this kind of stiffness distribution by hand, so an FEM model would do the trick.

Besides what HTURKAK said, it's possible that putting the beam on two elements, one stiff and one not stiff, will require use of a seismic amplification factor for vertical change in stiffness. The reason is that the stiffness is dramatically lower on the lower floor when you put a shear wall on a beam. A sketch might help if you have a specific situation. I find general theoretical ideas to work most of the time, but more often than not, a sketch will show a completely different situation than what I envisioned.