Uplift on CMU wall
Uplift on CMU wall
(OP)
I have a net roof uplift load of 15 psf (adhered roof) (06.D+W). The 40 foot steel roof joists bear on a bond beam in a CMU wall. The net uplift load on the wall will therefore be 40/2 x 15 psf = 300 plf. Without counting on mortar tension, it seems like I would have to engage (1/0.6 x 300 =) 500 plf of masonry to provide enough dead weight (or is it 1.5 x 300 = 450 plf?).
What is the best way to accomplish this?
Some options that I thought of:
Provide #4 vert @ 48" oc in grouted cores
Grout upper courses of block needed for dead weight.
Provide lower bond beam at elevation necessary to engage that much masonry dead weight. Provide vertical rebar from joist bearing elevation to lower bond beam.
Any other suggestions? What have others done in this situation? How many of you have ignored this requirement in the past?
What is the best way to accomplish this?
Some options that I thought of:
Provide #4 vert @ 48" oc in grouted cores
Grout upper courses of block needed for dead weight.
Provide lower bond beam at elevation necessary to engage that much masonry dead weight. Provide vertical rebar from joist bearing elevation to lower bond beam.
Any other suggestions? What have others done in this situation? How many of you have ignored this requirement in the past?






RE: Uplift on CMU wall
RE: Uplift on CMU wall
So the joist must be designed for the net wind uplift.
The joist connection to the wall must also.
The weight of a reinforced bond beam at the top of the wall (usually required by code anyway) can be used as counter weight to the uplift.
Reinforcing inside the wall to engage more of the wall below.
RE: Uplift on CMU wall
JAE is right on target in his statements.
Good luck.
RE: Uplift on CMU wall
The situation wasn't critical until the architect eliminated the stone ballast on the roof. The weight of the bond beam alone is not sufficient to resist uplift.
Thanks, JAE, for your confirmation to follow the load path thru!
The architect will not be happy, but then again he never is!
RE: Uplift on CMU wall
RE: Uplift on CMU wall
RE: Uplift on CMU wall
Remember to design the bond beam to resist the bending due to uplift between vert bars locations. I would not count on the mortar that attaches the bond beam to the next course below. Then I would just continue these vertical bars into the footing.
Is there shear on this wall?
RE: Uplift on CMU wall
It's my understanding that your wall works unreinforced for out-of-plane loads from wind. Don't you at least need some rebar to resist shear wall overturning, and also some jamb bars at openings?
RE: Uplift on CMU wall
I like the idea of the 2 couse bond beam.
Thanks to all!
RE: Uplift on CMU wall
RE: Uplift on CMU wall