masonry wall openings and out of plane loads
masonry wall openings and out of plane loads
(OP)
When designing a cmu wall with door/window openings in a high seismic area how should you distribute the lateral load from the area above the opening to the sides of the opening? How wide of a strip on either side of the opening do you assume will take the load?






RE: masonry wall openings and out of plane loads
Yes, the method sounds correct.
RE: masonry wall openings and out of plane loads
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: masonry wall openings and out of plane loads
So if I have a 30' long wall with with an 8 foot wide door opening, I can just assume the load is taken by a 4' wide strip on either side of the door and select steel accordingly?
RE: masonry wall openings and out of plane loads
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: masonry wall openings and out of plane loads
RE: masonry wall openings and out of plane loads
There would have to be a limit. In my opinion it wouldn't be reasonable to count on reinforcing steel that is say 10 feet away from an opening in an 8 foot tall wall.
It has always bothered me when codes don't address conditions such as this which is very common.
RE: masonry wall openings and out of plane loads
RE: masonry wall openings and out of plane loads
I looked in Masonry Design's guide (2nd edition) and the examples either have 'piers' with set dimensions, or they chose a dimension for the effective width without explanation. Also looked quickly at NCMA tech notes and nothing jumped out.
RE: masonry wall openings and out of plane loads
RE: masonry wall openings and out of plane loads
For wind I have always taken half the opening load to the jamb, plus the trib for the jamb, plus half the distance between the jamb and my resumed normal filled cell spacing. I rarely exceed 48" o.c. for minimum reinforcement though I know some engineers do, I have a hard time believing the CMU via mortar bonds (no intermediate bond beams) will span any further. This is probably conservative but...
With some buildings if the openings are large, wind loads are high, and maybe you also have floor loading above causing eccentric moments, we end up using 16" tie columns at many jambs. Also, if you have eccentricity at the floor/roof level to account for, this also gets concentrated in your jambs.
A more accurate procedure may be FEA similar to how PCA wall and other tilt programs work. However, unlike tilt which has a homogeneous thickness/rigidity, partially grouted CMU has a varying stiffness which would have to be accounted for in a program. I don't know of any such program to date.
RE: masonry wall openings and out of plane loads
RE: masonry wall openings and out of plane loads