Elevator Cores, Coupling Beams and Outbard Shear Walls
Elevator Cores, Coupling Beams and Outbard Shear Walls
(OP)
We have many projects where we have 2-3 PT floors of subteranean parking with 1-2 floors of PT above grade and then 5 floors of wood.
Most of these building have more than adequate shear provided in the perimeter basement walls and other exterior concrete walls.
The buildings also happen to have the usual concrete eleveator and stairwell cores.
When analyzing these structures they work without the core walls or with maybe the 3 sides that do not have openings in them.
The city reviewers require us to provide 100% shear walls with coupling beams around these cores (like a typical high rise construction project) even though they are not really needed for lateral resistance. We have done some with 3 shear walls and with lateral releases at the wall with the openings and they seem to be willing to accept that.
I am a little perplexed by this requirement and do not understand why we cant just do a normal wall at the core openings (even without releases)? I realize that these walls will not work laterally and may crack in a seismic event if the deflection is too great, but they have not been considered as part of the load path in the analysis and I would expect that we could make that decision without violating any code issues.
The reviewer hasn't been able to provide an explanation other than - thats just the way it is - and I am curios if anyone here could provide some insight.
Thanks!
Mark
Most of these building have more than adequate shear provided in the perimeter basement walls and other exterior concrete walls.
The buildings also happen to have the usual concrete eleveator and stairwell cores.
When analyzing these structures they work without the core walls or with maybe the 3 sides that do not have openings in them.
The city reviewers require us to provide 100% shear walls with coupling beams around these cores (like a typical high rise construction project) even though they are not really needed for lateral resistance. We have done some with 3 shear walls and with lateral releases at the wall with the openings and they seem to be willing to accept that.
I am a little perplexed by this requirement and do not understand why we cant just do a normal wall at the core openings (even without releases)? I realize that these walls will not work laterally and may crack in a seismic event if the deflection is too great, but they have not been considered as part of the load path in the analysis and I would expect that we could make that decision without violating any code issues.
The reviewer hasn't been able to provide an explanation other than - thats just the way it is - and I am curios if anyone here could provide some insight.
Thanks!
Mark






RE: Elevator Cores, Coupling Beams and Outbard Shear Walls
RE: Elevator Cores, Coupling Beams and Outbard Shear Walls
Mike McCann
MMC Engineering
RE: Elevator Cores, Coupling Beams and Outbard Shear Walls
You may want to try and justify your decisions based on specific clauses of the building code, and submit this as an appeal against the decision.
RE: Elevator Cores, Coupling Beams and Outbard Shear Walls
Good Luck!
RE: Elevator Cores, Coupling Beams and Outbard Shear Walls
I discussed this with Bijan Aalami of ADAPT (they design big towers all over the world) and he felt like it was completely unnecessary.
I was always taught that the design engineer selects a load path and so long as that is designed properly all the other components were simply redundant.
Relative stiffness is a good point and an exception to my statement above, but we have over 300 LF of shearwall (most of the surrounding basement walls) around the perimeter of the slab. I don't see any way the core would be stiffer unless you specifically design it to be stiffer.
Thanks for the feedback!
RE: Elevator Cores, Coupling Beams and Outbard Shear Walls
RE: Elevator Cores, Coupling Beams and Outbard Shear Walls
It is much simpler to disconnect the core from the diaphragm and design the walls for their own lateral loads due to their own weights. This should be the structural engineer's design call as long as it meets code, not the building official. I think that there is a whitepaper on a similar issue from SEAW and I will post it when I find it.
Mike McCann
MMC Engineering
RE: Elevator Cores, Coupling Beams and Outbard Shear Walls
Mike McCann
MMC Engineering