center of rigidity outside the building footprint
center of rigidity outside the building footprint
(OP)
An architect just submitted a floorplan with shearwall layouts such that the center of rigidity is outside the footprint of the building. Clearly that won't work, but what would actually happen in a lateral event? I am hoping someone can provide me with a straightforward explanation I could pass on to the architect.






RE: center of rigidity outside the building footprint
RE: center of rigidity outside the building footprint
RE: center of rigidity outside the building footprint
Mike McCann
MMC Engineering
RE: center of rigidity outside the building footprint
RE: center of rigidity outside the building footprint
RE: center of rigidity outside the building footprint
RE: center of rigidity outside the building footprint
RE: center of rigidity outside the building footprint
My response to the architect was to change the shear wall locations such that the COR was back inside the building, but I'd still be interested in exactly what reactionary problems this would create, in actual response to a lateral event.
RE: center of rigidity outside the building footprint
But when I twist the 2 perpendicular walls of the C shape to 45 degrees, the COR moves outside of the building like in your diagram. I do not follow how they are getting this.
RE: center of rigidity outside the building footprint
The polar moment of inertia is usually calculated after finding the COR when doing it by hand, and this takes into account any twisting affect on the shear walls.
RE: center of rigidity outside the building footprint
My 2 cents.
RE: center of rigidity outside the building footprint
RE: center of rigidity outside the building footprint
The help file says the following:
RE: center of rigidity outside the building footprint
For example, if there was only 1 shear wall at the top of the page (say the horizontal 60%E wall) then the centre of rigidity would be at the centerline of the wall.
Not if you add additional walls below this then this must by definition shift the center of rigidity down the page.
RE: center of rigidity outside the building footprint
RE: center of rigidity outside the building footprint
This building presents two different lateral situations, as is, it looks like a 3 sided box, turn it 45 degrees and it is closer to an L shape, but not quite because of the vector rigidities. Again, I probably would like to see different rigidities on the walls so that it looks less like a L shape in the one direct, but if given no chose, it still could be analyzed. I would recommend doing two sets of lateral checks though, one as is and one with the structure rotated 45 degrees. Then run the analysis as you would normally, apply direct shear to the COR, apply moment to the COR, with the summation of the two giving the total shear. If this was purely an L shape, it would be unstable, no moment arm to resist, but given the vector rigidity of the 45 degree walls, there would be small moment arms to produce moment resistance. In all likelyhood, you will have a torsional irregularity, which may or may not be acceptable, depending on code issues.
Again, I'm not a huge fan of this, not even a fan of three sided box layouts given there lack of redundancy, so this really comes down to engineering judgement.
RE: center of rigidity outside the building footprint
ssweetland, I agree about the unbalanced issues. that's my daily struggle with the architects - either windows everywhere or a house still standing after a hurricane (and more importantly, meeting code)!