Concrete Tilt-up Addition
Concrete Tilt-up Addition
(OP)
We are doing an addition to an existing 18 feet high concrete tilt-up building with a flexible roof diaphragm (See attached for layout). There is an existing re-entrant corner with its respective drag lines. Our addition consists of squaring off the building by adding to new walls.
My question is:
Is there a way to neglect the lateral resistance of the walls that make up the re-entrant corner and assume that the outer walls of the newly created box will resist the seismic loading?
My question is:
Is there a way to neglect the lateral resistance of the walls that make up the re-entrant corner and assume that the outer walls of the newly created box will resist the seismic loading?






RE: Concrete Tilt-up Addition
By adding the corner, you are increasing the lateral demand on the drag lines and associated shear walls so you'd have to simply check those with the added load.
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RE: Concrete Tilt-up Addition
Also, the diaphragm chord forces may or may not be impacted. Check those too.
Mike McCann, PE, SE (WA)
RE: Concrete Tilt-up Addition
Thank you for your input.
RE: Concrete Tilt-up Addition
1) If you can prove that the re-entrant walls would fail in a ductile fashion, you might be able to redistribute load out to your new walls. I'd think the odds of this working out to be pretty low.
2) If the individual wall segments of the re-entrant corner are stitched together to act compositely for lateral, you could remove that stitching and thereby reduce the stiffness of those walls. Folks on site may think that you've lost it.
The proportions of the building being what they are, I wonder if you might be able to justify rigid diaphragm behavior, even with an untopped steel deck. I'd think that a rigid analysis would shift a good deal of load away from the re-entrant corner walls.
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 Tilt-up Addition
In a way I was trying to avoid both, but given the existing conditions I won't be able to take any shortcuts and I will just have to analyze the re-entrant corner and drags for the additional loads.