Point Load on Concrete Wall
Point Load on Concrete Wall
(OP)
I have an Extremely thick reinforced concrete wall, around 6 feet thick and pretty tall as well, at least 15 feet.
I have to put a temporary concentrated load on the wall.
Owner's engineer wants the wall checked and suggested checking punching shear.
This made no sense to me, but the wall will be loaded near the edge, maybe 12"-16" in from the edge.
Other than bearing, I can't think of what else to check.
Intuitively I can see some sort of break out of the edge of the wall, similar to side face blowout.
Thoughts?
I have to put a temporary concentrated load on the wall.
Owner's engineer wants the wall checked and suggested checking punching shear.
This made no sense to me, but the wall will be loaded near the edge, maybe 12"-16" in from the edge.
Other than bearing, I can't think of what else to check.
Intuitively I can see some sort of break out of the edge of the wall, similar to side face blowout.
Thoughts?






RE: Point Load on Concrete Wall
The problem can occur if there is not enough horizontal steel near the point of application of applied load. Explained in attached pdf.
The formula for bursting force can be found in end block design in prestressed concrete Codes in any country or any text book.
RE: Point Load on Concrete Wall
What seems counterintuitive is that the failure plane that makes sense (what is drawn in the sketch) is a principal compression plane, not a principal tensile plane.
RE: Point Load on Concrete Wall
RE: Point Load on Concrete Wall
In all seriousness I just did some design calcs on something similar, what kind of load are we talking about? The failure mode is as Norm's sketch shows, and I have a method from a textbook for the design of the rebar for such a failure. Its not too bad at all.
RE: Point Load on Concrete Wall
I am estimating the load at 45 kips, for now (WAG).
Care to share your textbook method. I cant find anything in my concrete texts.
RE: Point Load on Concrete Wall
Any takers now?
RE: Point Load on Concrete Wall
RE: Point Load on Concrete Wall
Look at ACI 318-05 Section 18.13
RE: Point Load on Concrete Wall
Now would be great~!
RE: Point Load on Concrete Wall
do you think that directly applies here?
RE: Point Load on Concrete Wall
RE: Point Load on Concrete Wall
Force W can be resolved into component parallel and perpendicular to the failure plane. Parallel component is Wcosθ. Length of failure surface is 12/sinθ.
The shear stress on the failure plane is Wcosθsinθ/(a + b/2)L. This will be maximum at 45 degrees. Compare that value with allowable shear for plain concrete.
BA
RE: Point Load on Concrete Wall
BA
RE: Point Load on Concrete Wall
BA
RE: Point Load on Concrete Wall
Thank you kindly for the input.
I will run some numbers.
RE: Point Load on Concrete Wall
BA
RE: Point Load on Concrete Wall
Should'nt the shear stress be {W*sinθ}/{cosθ*(a+b/2)L}
RE: Point Load on Concrete Wall
I don't think so. See attached.
BA
RE: Point Load on Concrete Wall
RE: Point Load on Concrete Wall
and the question becomes, what shear allowable to use?
RE: Point Load on Concrete Wall
I did not expect the angle to be 45 degrees but the expression cosθsinθ is maximum at 45 degrees.
The suggested formula does not take into account the shearing resistance at the two ends of the failure zone, so the failure angle could change as a result.
slick,
Okay.
BA
RE: Point Load on Concrete Wall
Engineering Judgement??
Kieran
RE: Point Load on Concrete Wall
Yes, I think it is conservative. The two end areas combined are (a + b/2)^2/tanθ so a revised angle could be calculated based on this additional shear resistance.
Vc is defined in the Canadian code. Fifty percent of Vc is permitted when shear reinforcement is omitted. I would think similar provisions can be found in ACI.
BA
RE: Point Load on Concrete Wall
You may be right. My first thoughts were to simply check the bearing stress and forget about it, but in this case the client wants the issue specifically addressed, so we have been attempting to come up with a way of doing that.
BA
RE: Point Load on Concrete Wall
I think the location of the load is more important here compared to the thickness of the wall. If the load was smack on the center, I agree with you.
RE: Point Load on Concrete Wall
My thoughts were originally the same,...however, I can't simply plop a 45 kip load right near the edge of the wall. The wall could be 5 miles wide at that point but I still can't load the edge without running some numbers.
slick-
Think phi x 2 x fc'^0.5 is the correct shear formula?
RE: Point Load on Concrete Wall
RE: Point Load on Concrete Wall
RE: Point Load on Concrete Wall
RE: Point Load on Concrete Wall
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RE: Point Load on Concrete Wall
RE: Point Load on Concrete Wall
Slick's attached method is the same I use from an older concrete text. I think a few bars in the right spot are cheap insurance. I do this even on embed connections in tilt walls that rely on bearing.
RE: Point Load on Concrete Wall
I never thought to look at PCA until Saturday....I still can't find my notes from '02.
Guess I should get the new ones.