ACI Chapter 17 - Composite Flexural Members - Spread Footing

[GerryBertier]

I have a situation where the concrete contractor placed footing too thin. Instead of the specified 13'x8'x1'-6", it is 13'x8'x1'-0".

Punching shear, one-shear and flexure in both directions do not check.

I'm thinking of doing a grid of #3 U-Stirrups (or U-dowels / hairpins) to transfer horizontal shear between placements at the horizontal cold joint.

A couple of issues I have:
- Simpson and Hilti adhesives require 12" embedment for full development. Is there a way I can provide a percent of this embedment, by increasing my provided steel? I can base the percentage on Appendix D numbers relative to ultimate steel strength in tension. Make the U-strippups spaced far enough apart to not overlap breakout cones. Then increase my joint steel, which would decrease sustained tension in each dowel.

- In relation to the adhesive above, I suppose the adhesive is in sustained loading, since its an isolated footing with gravity loads - correct? Is this a good idea - adhesive under sustained load?

- In regards to horizontal shear, my Vuh at the joint (which is use in ACI 17.5.3) is actually the sum of components of shear flow (at that distance away from the column) due to bending in two directions since they are acting concurrently? - correct?

- Lastly, what is the minimum development for the hoop portion of the dowel? I'm looking at PCA Notes 318-11, sheet 12-12, and see no requirement.

 

[KootK]

- ACI requires full development of the dowels either side of the joint with no allowance for prorating.

- They have some alternate methods for this kind of thing in other parts of the world. Call you local Hilti rep, tell him or her what you're up to, and I'm sure they'll point you in the right direction.

- Agree with adhesive under sustained loads but, if you're using the Euro methods, I think it's more of a true shear dowel thing than shear friction so probably a pass there.

- Agree with bidirectional additive.

- I'm not sure that the hoops actually get you anything that standard 90 don't provide from a code standpoint. As such, I probably wouldn't do hoops.





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.

 

[Ingenuity]

I'm thinking of doing a grid of #3 U-Stirrups (or U-dowels / hairpins)

Keep in mind, from a practical installation standpoint, U-stirrups are a bit of a pain to install. First, the drill hole pairs have to be in close tolerance (spacing and vertical), and second, adhesive anchored anchors/rebars require a 'twisting/rotation action' of the installed anchor/rebar after the hole is partially filled with resin: U-bars make such a installation impossible. Go with hairpins.

 

[GerryBertier]

I've decided to recommend just removing the footing and replacing it with the correct thickness.

Even if Hilti can provide me development in less than 9", and I use the ACI 12.13.2.1 by providing a longitudinal bar through every hook (I only have 6" overlay which doesn't meet 6" min hook dev), I'm calculating #3 at a 5" OC grid, which is just unreasonable.

My column load is a little less than 300 kips, so its nothing to mess around with.

 

[hokie66]

The right choice. The only other solution I would have entertained would be to cast your 18" footing on top of the deficient one...if you had enough depth to the finished surface.