Isolating CMU Walls in Seismic Regions
Isolating CMU Walls in Seismic Regions
(OP)
Hello everyone, I have a follow up question to the problems posed in thread507-332796: Masonry Stair Walls and Connection to Primary Structure .
As PicoStruc pointed out in the thread, CMU walls pose a problem when trying to isolate them from the lateral force resisting system because if they're not properly isolated they add stiffness to the building (and could affect the R value).
In my instance, I have a 3-story building in SDC D with predominantly light gauge metal stud walls, with CMU elevator cores and CMU first floor exterior walls. I have accounted for the CMU wall weight in the effective seismic weight, but have designed the LFRS with the CMU walls not participating and the light gauge shear walls resisting the entirety of the load.
To get to the point, my questions are:
1) Are horizontal slip connections enough in the perimeter CMU walls to not transfer the lateral force?
2) Can the CMU elevator cores be designed as free-standing (spanning horizontally and supporting themselves)such that a connection to the floor is not needed?
3) AISI-400: Section E2.2.4 Seismic Load Effects Contributed by Masonry or Concrete Walls. "...light frame shear walls...are permitted to be used to provide resistance to seismic forces in buildings and other structures with masonry or concrete walls, provided the following reqts are met". Meeting none of the allowed requirements, am I still in compliance if I isolate the walls from the structure laterally in either case above? What exactly are the load effects contributed by the masonry walls?
Surely, this can't be a blanket statement meaning IF masonry or concrete even EXISTS, you can never use light frame shear walls.
4) PicoStruc mentioned that the CMU walls could not be used in gravity bearing as well. Does anyone know the logic behind this exclusion?
Any and all input is appreciated.
As PicoStruc pointed out in the thread, CMU walls pose a problem when trying to isolate them from the lateral force resisting system because if they're not properly isolated they add stiffness to the building (and could affect the R value).
In my instance, I have a 3-story building in SDC D with predominantly light gauge metal stud walls, with CMU elevator cores and CMU first floor exterior walls. I have accounted for the CMU wall weight in the effective seismic weight, but have designed the LFRS with the CMU walls not participating and the light gauge shear walls resisting the entirety of the load.
To get to the point, my questions are:
1) Are horizontal slip connections enough in the perimeter CMU walls to not transfer the lateral force?
2) Can the CMU elevator cores be designed as free-standing (spanning horizontally and supporting themselves)such that a connection to the floor is not needed?
3) AISI-400: Section E2.2.4 Seismic Load Effects Contributed by Masonry or Concrete Walls. "...light frame shear walls...are permitted to be used to provide resistance to seismic forces in buildings and other structures with masonry or concrete walls, provided the following reqts are met". Meeting none of the allowed requirements, am I still in compliance if I isolate the walls from the structure laterally in either case above? What exactly are the load effects contributed by the masonry walls?
Surely, this can't be a blanket statement meaning IF masonry or concrete even EXISTS, you can never use light frame shear walls.
4) PicoStruc mentioned that the CMU walls could not be used in gravity bearing as well. Does anyone know the logic behind this exclusion?
Any and all input is appreciated.





