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CONCRETE SHEAR WALL & BUILDING FRAME

CONCRETE SHEAR WALL & BUILDING FRAME

(OP)
I have asked this question several weeks ago on irregular building. I got some valuables inputs but were not able to put them into my design analysis as I still have no way to go further due to lack of confidence.

I am designing an L-shaped building that has to resist earthquake forces.
My 1st try, assumed column sizes are the same ; 450mm x 450mm, I computed the base shear and the resulting horizontal earthquake forces to be applied on the frames seem too large. Obviously the results are so largely due to large eccentricity where torsional moment contributed much to the hor forces on the frame. The top floor takes resulting hor force about 100+ KN and decreases as it goes down the floor.
I have just gone through some reference which seem to direct me to using reinforced concrete shear wall as a better option rather than building separation.
2nd try, I subjectively combined shearwall and columns in the calculations of stiffness and deflection and finally the hor. forces on the portal frames. The hor. forces on the column-beam frame seem to very small (35KN max) compared to my 1st try while the shear wall takes larger forces (230KN at the top. The resulting hor forces, in my view, are attracted more by the shear wall because of its higher stiffness.
Is my 2nd try correct when we use shear wall to account for earthquake forces along with column-beam frames or the forces should simply be distributed on the shear wall and assume no hor forces applied to the column-beam frames (Consequently column-beam frames are assumed to be non-Structural resisting frames)?

RE: CONCRETE SHEAR WALL & BUILDING FRAME

Yes, for shear wall buildings, designers often do assume that the column/beam frames do not contribute laterally because the shear walls dominate from a stiffness perspective. Once upon a time, I a saw a recommendation that if the shear wall load path in a given story was at least six times as stiff as the alternate load paths combined, then the alternate load paths could be disregarded. I have no idea where I saw that however. There are some situations, such as dual systems in seismic country, where other considerations may govern the assumed participation of your beam/column frames.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: CONCRETE SHEAR WALL & BUILDING FRAME

In the US, the ACI code requires that non-participating frames need to be designed/detailed for the drift in high seismic design classes. I imagine that this exists elsewhere too.

"It is imperative Cunth doesn't get his hands on those codes."

RE: CONCRETE SHEAR WALL & BUILDING FRAME

(OP)
Thanks a lot Mr. Kootk. I am not sure if the shear wall in the building can take all the lateral load by neglecting the participation of column-beam frames because, due to architectural demand, the max width of the wall would be limited to 2.5m on each outermost side along the shorter side and two 2.5m walls on each side along the longer side of the bldg (4 walls on this side).
I tried to neglect the column-beam frames participation but resulting lateral forces on the shear walls seem large.
Appreciate your additional advice Mr. MacGruber22. Could you please give the specific version of ACI? I am not in US but I studied in the Philippines which has structural codes patterned mostly from ACI/ASCE/SAE and little on others.

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