Elevator Shaft Shear Wall - NYC Brownstone
Elevator Shaft Shear Wall - NYC Brownstone
(OP)
Other NYC structures guys may be familiar with this situation. I have a project combining two 5-story brownstones, knocking out the middle party wall, re-framing each floor level and adding a new conc/cmu elevator core (13'x22'). Now the shaft needs to be designed to resist the total seismic lateral forces, which, after based on NYC seismic code, the factored design moment at base= 8,400 k-ft. So far my numbers show that I can get a 10" thick conc. wall to work with (8)#9 bars at the corners. Now as I move up the shaft, the architect wants 8" CMU walls. So, I'm looking at switching to 8" CMU at the 3rd floor where the design moment drops to around 5,000 k-ft which will require roughly (6) #6 bars at each of the corners of the shaft.
Sorry for the long story but, for you veterans of CMU and shear wall design out there, is this asking way too much from a CMU elevator shaft? Is it possible to bundle the #6 bars in 8" CMU?
Any and all input is appreciated..
Sorry for the long story but, for you veterans of CMU and shear wall design out there, is this asking way too much from a CMU elevator shaft? Is it possible to bundle the #6 bars in 8" CMU?
Any and all input is appreciated..






RE: Elevator Shaft Shear Wall - NYC Brownstone
RE: Elevator Shaft Shear Wall - NYC Brownstone
RE: Elevator Shaft Shear Wall - NYC Brownstone
A lot would depend on the location of the new elevator core in relation to the combined structure. The core placed symmetrically about the combined structure is desirable. The core located at the perimeter would be problematic. What is the new floor system / framing? The new floor system will have to transfer the lateral load to the core through a combined action of diaphragm + collectors. You mentioned the shaft needs to be designed to resist the total seismic lateral forces? Of course, you can design conservatively, but then what was the LLRS earlier?
As far as reinforcing goes..... I don't know which code you follow. I have ACI 530-05. Chapter 3, section 3.3.3.1 gives the bar size in relation to member thickness, least dimension of the cell, and area of the cell. But codal provisions apart, we always reduce it further by two sizes; max #8 in 10" wall, max #6 in 8" thick wall. We have never used anything more than #8 rebar in masonry construction. We try to restrict the projections of the bars above the slab preferably to less than 3'- 6" from block placement point of view.
Per section 3.3.3.6, bundling of the bars is not permitted. We don't ever attempt welding of rebars or use of couplers.
Why place everything at the ends? In design, we account for all the vertical reinforcing. This way rebars required at the ends can be significantly reduced. You mentioned 8 - #9 at corners. Do you have return flanges along the elevator doors? If not, insist on it, that would help in the placement for 13 feet walls.
RE: Elevator Shaft Shear Wall - NYC Brownstone
RE: Elevator Shaft Shear Wall - NYC Brownstone
RE: Elevator Shaft Shear Wall - NYC Brownstone