how to make sure concrete wall doesn't take shear in a frame
how to make sure concrete wall doesn't take shear in a frame
(OP)
This has confused me for a while. I have a concrete frame with beams and columns (2'-3' SQ). I am detailing concrete walls (9") flush with the outside face of columns. All wall reinforcement will have a developed hook in columns/beams.
My question is: If I am only designing the concrete walls for out-of-plane loads, does it mean I am being un-conservative because I am ignoring the in-plane shear force potentially in the walls from the beams and columns? How do you typically design for this?
Thank you.
My question is: If I am only designing the concrete walls for out-of-plane loads, does it mean I am being un-conservative because I am ignoring the in-plane shear force potentially in the walls from the beams and columns? How do you typically design for this?
Thank you.






RE: how to make sure concrete wall doesn't take shear in a frame
Design the rebar to span across the expansion joints for the out-of-plane loads.
Depending on the wall height and out-of-plane loading it may be easier to design the walls as cantilever off of the floor structure and not fasten them to the frame at the sides and top at all.
RE: how to make sure concrete wall doesn't take shear in a frame
RE: how to make sure concrete wall doesn't take shear in a frame
Whether or not ignoring the wall's contribution is conservative is a murky issue. On the one hand, the wall's presence may draw load from other hard working frame elements. On the flip side, the wall may present a detrimental torsional irregularity if not detailed to be isolated from the intended lateral system.
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: how to make sure concrete wall doesn't take shear in a frame
For people that is familiar with STAAD, would you use "surface" elements with "offset" to model the walls? (Is it possible to set "offset" with "surface" elements"?)
Thanks!
RE: how to make sure concrete wall doesn't take shear in a frame
I'll assume that you're still planning to cast the walls and columns monolithically as you described initially. In that case, some consequences off the offset are:
1) Shear in the wall will be delivered as axial force to the columns off of the column center lines, resulting in some additional moments to be considered in the columns.
2) Technically, the shear center of the column/wall assembly will outboard of the exterior side of the wall, similar to how it works with steel channel shapes. I wouldn't sweat the impact that this will have on your overall distributions of load throughout the structure however. The inaccuracies that we accept in performing elastic analysis more than outweighs any inaccuracy in the determination of the wall assembly shear center.
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: how to make sure concrete wall doesn't take shear in a frame
RE: how to make sure concrete wall doesn't take shear in a frame
Sorry Rainbow, I'm not clear what you're asking hear. Can you elaborate?
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: how to make sure concrete wall doesn't take shear in a frame
RE: how to make sure concrete wall doesn't take shear in a frame
If it were a really serious structure I would have fought to make the walls independent, but the Owner didn't want any joints or gaps due to hygiene reasons.
RE: how to make sure concrete wall doesn't take shear in a frame
RE: how to make sure concrete wall doesn't take shear in a frame
1) As I mentioned above, inaccuracy in the location of the wall shear centre gets lost in the noise of more significant approximations that we make. One such approximation commonly used in modelling concrete is linear elasticity. Park and Paulay point this out in the shear wall section of their classic concrete book.
2) Presumably, you've got lateral resisting elements spread about your building that are separated by distances that are very large relative to the shift in shear center of your wall assembly. Therefore, an error in the location of the wall assembly shear center will not materially affect how your loads distribute to the various lateral load resisting elements present.
3) In your wall assembly, part of the stiffness is associated with flexural deformation and part is associated with shear deformation. The portion associated with shear deformation will remain close to the centreline of the wall no matter what interconnectivity is created with the adjacent columns. And, the squatter the wall, the more important a role shear deformation plays.
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.