Concrete Edge Load / Direct Shear

[theonlynamenottaken]

I was asked to review another's design for attachment to an existing concrete curb. The 5000# load is for direct suspension of personnel. See sketch.

My initial response was that you wouldn't want to load a curb that close to a free edge in this fashion. The designer wants this backed up by calcs. His calcs use ACI 11.12 two-way shear, using d = 4". (see the longer, downward crack)

I argued that it couldn't be considered reinforced, which I believe is obvious, and that a failure could likely look like the upper, shorter crack in the sketch.

Thoughts? Furthermore, how would you back it up with calcs?

 

[theonlynamenottaken]

Oops. Forgot to re-pdf with the second crack drawn in.

 

[msquared48]

Why don't you put a steel bearing plate under the nut of sufficient size so that the smaller crack does not happen, and the developed shear cone is larger?

I do agree that the section is not properly reinforced for shear currently.

With regard to the calcs, I would just use root f'c times the most likely cone surface area to develop for the available resisting shear force.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[JAE]

You also can't show by ACI that the curb won't fail in direct shear at its interface with the floor. The vertical #4 bars must be fully developed into the curb (i.e. hook or full development length) to create the necessary shear friction between curb and floor.