Concentrated Load on CMU Wall
Concentrated Load on CMU Wall
(OP)
Just wanting to confirm my interpretation of the code for a masonry question I have. For reference, I'm currently looking at the 2008 masonry design code, so I know the verbiage will be slightly different between years.
My condition involves a steel beam bearing on a plate which sits atop a CMU wall with a running bond. In checking the capacity of this bearing condition, my design will include 1) the bearing check of the concentrated load on the CMU and 2) the effective wall panel itself resisting the compression load.
For part 1, section 1.9.5 (2008 version) notes that the bearing area is a function of the loaded area and any distribution for a concentric load. For simplicity, if my bearing plate is the full width of the wall, I would think that taking the concentrated load divided by the baseplate area would be the value to compare against 0.25*f'm.
For part 2, section 1.9.7 (2008 version) describes a distribution of a 2:1 slope to half height of the wall. Again for example a 10' high wall with a 12" wide baseplate would give an effective length of 12" + 2*(60/2) = 72". With this in mind I could take my concentrated load and check a 72" wide wall panel to resist it. This would obviously change if the 2:1 distribution is truncated by a wall end or adjacent load.
Anyone want to chime in on this? My main concern here is resisting the bearing load of a large concentrated force. Seems like the only solution for a really big load would be increasing the baseplate size significantly or bumping up my f'm?
Thanks!
My condition involves a steel beam bearing on a plate which sits atop a CMU wall with a running bond. In checking the capacity of this bearing condition, my design will include 1) the bearing check of the concentrated load on the CMU and 2) the effective wall panel itself resisting the compression load.
For part 1, section 1.9.5 (2008 version) notes that the bearing area is a function of the loaded area and any distribution for a concentric load. For simplicity, if my bearing plate is the full width of the wall, I would think that taking the concentrated load divided by the baseplate area would be the value to compare against 0.25*f'm.
For part 2, section 1.9.7 (2008 version) describes a distribution of a 2:1 slope to half height of the wall. Again for example a 10' high wall with a 12" wide baseplate would give an effective length of 12" + 2*(60/2) = 72". With this in mind I could take my concentrated load and check a 72" wide wall panel to resist it. This would obviously change if the 2:1 distribution is truncated by a wall end or adjacent load.
Anyone want to chime in on this? My main concern here is resisting the bearing load of a large concentrated force. Seems like the only solution for a really big load would be increasing the baseplate size significantly or bumping up my f'm?
Thanks!






RE: Concentrated Load on CMU Wall
RE: Concentrated Load on CMU Wall
RE: Concentrated Load on CMU Wall
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Concentrated Load on CMU Wall
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Concentrated Load on CMU Wall
I agree with your reading of the code sections FYI.
RE: Concentrated Load on CMU Wall
RE: Concentrated Load on CMU Wall
I had a similar discussion with a young engineer who was finding that the longer she made the bearing plate under a beam (parallel to the wall) the thicker the plate needed to be. I tried to convince her that no matter HOW long she made the plate, most of the forces will be concentrated right under the load and most the plate wouldn't "activate". The same for me is true with column base plates.
RE: Concentrated Load on CMU Wall
I did an FEM investigation of this way back and came to the same conclusion. Base plate thickness need to be ridiculous in order to generate anything resembling a uniform bearing pressure. I've come to accept that some degree of material crushing below the base plate hot spots is required to allow these things to function successfully.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.