Shear Friction

[Hercul3s]

Hi All,
I have to design for shear friction to transfer base shear forces from "collector grade beams" (at the base of lateral frames), back into my slab on grade.
The beams are not imbedded into the slab - the slab sits on the beams, so to me, this is an issue of shear friction. The problem is that the Architects want to run waterproofing on top of my grade beams and pile caps, so I can't count on the coefficient of friction "Miu" or lambda, as per ACI318-08 Sect. 11.6.4 (11.6.4.3) or ACI318-14 Sect. 22.9 (Table 22.9.4.2). It seems I'll have to work with the shear capacity of steel rebar alone. What's your opinion: Would you use 0.4fy for the shear capacity of rebar crossing the shear plane? Or suggest another method to use?
Thanks in advance!

 

[jayrod12]

I would suggest the architect runs the waterproofing around your gradebeam. That seems like the easiest start.

 

[phamENG]

What does their waterproofing detail look like? Bell type? Adhered hydrophilic strip? In most of the details I've used shear friction is still feasible. After all, it's not an issue of contact area - it's an issue of "normal force" (rebar tension capacity not actively engaged in resisting tensile stresses) and your coefficient of friction. Your coefficient of friction may take a beating to keep the concrete smooth enough for the waterstop to be effective, but you still have friction there - ACI provides coefficients for a range of surface conditions.

Or, as jayrod12 suggested, you can see if they can change their detailing. Bentonite sheets could be applied to exterior surface of the grade beam/slab junction and do the job that way (these are pretty common on basement and elevator pit walls).

 

[Hercul3s]

We don't have details for the waterproofing yet - it's maybe too early for that. Right now the instructions are to "consider waterproofing between beam and slab".
I agree with both of you, jayrod12 and phamENG: running the waterproofing down the sides of the beam and sealing it should be enough, but...

Right now I'm looking at ACI318 Appendix D, on Anchoring to Concrete. Even though this is for anchors, I may be able to use ASTM rebar fy and fu, in place of fu_ta.
This is my best guess so far!

I'll still suggest running the wp down the beam sides. I hope they'll accept that solution!

Thanks guys!

 

[phamENG]

Check out this Link for some hydrophilic waterstop info. These are probably the most popular - they're the "easiest" to install, have a minimal impact on rebar detailing, and they're pretty cheap. I say "easiest" because they're also the easiest to screw up.

You're probably okay to continue with shear friction. Appendix D (or Chapter 17 if your code has adopted ACI 318-14) is not applicable for rebar. The behaviors are not the same. If you were absolutely desperate you may be able to come up with some comparison between deformed bar development with adhesive anchor bond to concrete. But I doubt it - and wouldn't use it as part of the lateral force resisting system. Waterproofing between slab and grade beam is not likely to occupy the entire interface - only an inch or two. So you'll still have shear friction.