Point load distribution through a CMU wall to a footing
Point load distribution through a CMU wall to a footing
(OP)
When a point load is applied to a typical CMU foundation wall that only has dur-a-wall horizontal reinforcing, how much of the footing captures the load.
For example, If I apply a 10000 pound load on the top of a CMU wall that is 8 feet high, the load spreads outward as it travels down through the wall and is transferred to the substrate or soil by a certain amount of footing. How many linear feet of this footing will capture the load?
For example, If I apply a 10000 pound load on the top of a CMU wall that is 8 feet high, the load spreads outward as it travels down through the wall and is transferred to the substrate or soil by a certain amount of footing. How many linear feet of this footing will capture the load?






RE: Point load distribution through a CMU wall to a footing
If you are planning on using arching action be cautious with respect to control joint location since you can not have the arch affect through the control joint.
RE: Point load distribution through a CMU wall to a footing
RE: Point load distribution through a CMU wall to a footing
That applies ONLY to the wall design itself. The question is how much to put on the footing below.
We use the section you refer to for the wall but assume a maximum 45 degree spread for the footing designs.
RE: Point load distribution through a CMU wall to a footing
RE: Point load distribution through a CMU wall to a footing
RE: Point load distribution through a CMU wall to a footing
RE: Point load distribution through a CMU wall to a footing
Does this mean that for a 30' tall x 8" thick cmu wall with joists spaced at 6' o/c you would put a series of spread footings in below the joist bearing locations? Or would you widen the entire strip footing underneath the wall based on the ACI 530 effective width for the design of a wall pier?
RE: Point load distribution through a CMU wall to a footing
ACI 530 doesn't apply to footing design in any way.
In reality the footing will see a dispursed load over a very wide area (assuming running bond). I could see 30 degree spread (vs. my 45 degree) but limiting your footings to 4T seems very, very conservative.
RE: Point load distribution through a CMU wall to a footing
RE: Point load distribution through a CMU wall to a footing
RE: Point load distribution through a CMU wall to a footing
BA
RE: Point load distribution through a CMU wall to a footing
RE: Point load distribution through a CMU wall to a footing
RE: Point load distribution through a CMU wall to a footing
RE: Point load distribution through a CMU wall to a footing
You should have a bond beam at the top of any CMU wall anyway, but I am not sure I count on that to spread the load out much... The stiffness you get from the height of a CMU wall is what is helping you. This is usually more of a concern in lintel design over window and door openings.
I second Shobroco's comment, I'd be way more concerned with the masonry design of a 30ft tall wall, are we talking about laterally unbraced??! A large concentrated axial load with some eccentricity should be causing you all kinds of problems unless we are talking a two story building with a floor bracing at mid-height.
But as far as axial load distribution to a strip footing, I don't give it much thought if the wall is solid (I mean no openings, not solid grouted), and 10ft tall or more, unless the reactions are VERY large, and then you may have a concrete tie column anyway (see below)...
Times to be concerned with widening a strip into a mini-pad footing due to high concentrated loads, in my experience:
-tilt-up panels with small panel legs
-CMU with small piers/jambs created by wall returns, corners, expansion joints, or other openings
-concrete tie column embedded in a CMU wall supporting a large load from a girder (even though there will be load sharing into the adjacent CMU unless you have joints, my gut tells me the tie column will "attract" more axial load so I am conservative there)
HTH..
RE: Point load distribution through a CMU wall to a footing