Unreinforced Masonry Wall Stresses
Unreinforced Masonry Wall Stresses
(OP)
When an unreinforced masonry wall goes from no grouting to partial grouting, the compressive stress from any axial load (live or dead), should go down, as An increases correct?
In lieu of this, if I want to maximize my vertical compressive stress to offset tensile stress from flexure in the grout (from out of plane loading) it seems that adding grouting would not be the solution.
At the moment my wall is failing because the flexural tensile stress in the grout is above the limit, now, by grouting some cells, it actually has an offsetting effect on the net stress because the additional grout lowers my compressive stress, which I was subtracting off my flexural tensile stress, however it does lower my flexural tensile stress as well... the key is figuring if flexural tensile stresses lower enough such that the decrease in compressive stresses don't put me in an overstress condition still ... per table 2.2.3.2 in the ACI 530-05.
After my analysis I found that as I add grout, the wall tensile stresses do go down as the section modulus increases, however, the net effect from the dead load stress doesn't help my overall net tensile stresses as much. Therefore, if I were to fully grout my wall I'm finding that I still need to add steel reinforcing.
Is this an appropriate analysis?
In lieu of this, if I want to maximize my vertical compressive stress to offset tensile stress from flexure in the grout (from out of plane loading) it seems that adding grouting would not be the solution.
At the moment my wall is failing because the flexural tensile stress in the grout is above the limit, now, by grouting some cells, it actually has an offsetting effect on the net stress because the additional grout lowers my compressive stress, which I was subtracting off my flexural tensile stress, however it does lower my flexural tensile stress as well... the key is figuring if flexural tensile stresses lower enough such that the decrease in compressive stresses don't put me in an overstress condition still ... per table 2.2.3.2 in the ACI 530-05.
After my analysis I found that as I add grout, the wall tensile stresses do go down as the section modulus increases, however, the net effect from the dead load stress doesn't help my overall net tensile stresses as much. Therefore, if I were to fully grout my wall I'm finding that I still need to add steel reinforcing.
Is this an appropriate analysis?
Scott






RE: Unreinforced Masonry Wall Stresses
For simple low rise situations I would neglect self-weight altogether when looking at the flexural stresses in a wall.
You are finding out that hollow CMU doesn't have much flexural strength. It sounds like you will need make yours a reinforced wall.
RE: Unreinforced Masonry Wall Stresses
BA
RE: Unreinforced Masonry Wall Stresses
And now I will be climbing into my horse and buggy
DaveAtkins
RE: Unreinforced Masonry Wall Stresses
/Facepalm. I was just looking at that. Now the note that describes interpolation, as it referes to percentage, what do people typically do, take the full length of wall ... count up grouted and ungrouted cells, and do the division and interpolation from there. Or is there a different way that is more standard. I guess that seems the most obvious to me.
Scott
Scott
RE: Unreinforced Masonry Wall Stresses
RE: Unreinforced Masonry Wall Stresses
RE: Unreinforced Masonry Wall Stresses
BA
RE: Unreinforced Masonry Wall Stresses
DaveAtkins
RE: Unreinforced Masonry Wall Stresses
Curious as to where URM design is still occurring and what are these structures?
RE: Unreinforced Masonry Wall Stresses
95% of the existing schools are unreinforced load bearing masonry. Many dating back to the 1910's.
RE: Unreinforced Masonry Wall Stresses
RE: Unreinforced Masonry Wall Stresses
Shear walls are Plain Unreinforced Masonry. Interior non load bearing are unreinforced.
Chicagoland area.
We detail #4 Dowels @ 48" OC for the required mechanical connection to the foundation per IBC 2009. We didn't do this up until IBC 2009. No mechanical connection hasn't created any problems. Concrete masonry is concrete, foundation wall is concrete. Empirically no problems. We've had lengthly discussions concerning this and its hard to justify to the owner (since we haven't been for some time). Ultimately we decided it would be a good practice (and to code obviously).
Existing schools tend to be 2'-0" multi wythe load bearing brick. All of the 8" load bearing masonry my firm has done in the last 20 years is holding up well and we haven't had any problems.
Most of the owners we work with over long periods of time. We work with architects which tend to rotate school districts throughout time, but we work with most of the architects, so we end up seeing our work down the road.