Point Load on Concrete Wall

[ToadJones]

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?

 

[ToadJones]

This is also ignoring a shear plane perpendicular to the one show in the sketch, so it is conservative, right?

and the question becomes, what shear allowable to use?

 

[BAretired]

Toad,

I did not expect the angle to be 45 degrees but the expression cos[θ]sin[θ] 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

 

[kieran1]

I think this is clearly a case of over analysing. If a 6 feet thick concrete wall is not capable of supporting this load then we all need help.
Engineering Judgement??

Kieran

 

[BAretired]

Toad,

Yes, I think it is conservative. The two end areas combined are (a + b/2)^2/tan[θ] so a revised angle could be calculated based on this additional shear resistance.

V_c is defined in the Canadian code. Fifty percent of V_c is permitted when shear reinforcement is omitted. I would think similar provisions can be found in ACI.

BA

 

[BAretired]

Kieran,

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

 

[slickdeals]

@Kieran,
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.

 

[ToadJones]

Kieran-
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?

 

[USCeng09]

I'm not sure if this meets all of your design criteria but I would take a look at PCA Notes on ACI 318-05 Example 14.2 on Page 14-9. Good luck! Let me know if you need a copy of the page

 

[ToadJones]

a copy would be nice

 

[slickdeals]

See attached

 

[USCeng09]

http://files.engineering.com/getfil...2dd6-4e48-83b2-682bdf78c1ac&file=IMG_0344.jpg

http://files.engineering.com/getfil...c7d1-4943-8f10-dcf93d3c0560&file=IMG_0346.jpg

http://files.engineering.com/getfil...d02a-4be9-8445-89ce0ea39ec7&file=IMG_0348.jpg

 

[ToadJones]

that you slick.

 

[a2mfk]

Sorry Toad, my weekend got away from me...

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.

 

[ToadJones]

thanks guys.
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.