Shear Friction at Moment Joints (base of Fixed walls)

[Everynameistaken]

thread507-418612

Hello,

I was looking up the shear transfer at the base of a retaining wall and came across this thread and was looking for peoples thoughts.

I have a very heavily loaded tall wall that is fixed at the base. The wall is 1.2m thick and has +/- 10,000mm2/m of reinforcing for flexure at the base. The wall requires shear ties with 15M legs every 600mm in plan and 300mm along the length.

The shear at the base of the wall is very high and looking and interface shear transfer to get the shear into the footing. My question comes from the reference in the ACI codes (318 or 350) when talking about the use of the flexural bars in the interface shear calculation.

If I have already counted on the area of these bars for flexure am I not double dipping if I use them for interface shear as well? I understand there is a couple between the reinforcing and concrete stress block which creates a net zero compression on the joint and I have the self weight of the wall and whatever it is supporting as the net compression. If the system ever applys this load in the wall (seismic) then I will have the tension in the bars (for flex) already so how to I ensure I do not yield these bars when adding interface tension as the small net compression is not enough for interface?

Thanks

 

[DaveAtkins]

You are not double dipping when you use flexural tension bars for both flexure and shear friction. This is because the friction at the compressive stress block resists the shear.

DaveAtkins

 

[KootK]

I agree with Dave on the double dipping. That's one heck of a retaining wall.

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.

 

[Everynameistaken]

Yes It sure is a big wall!

It is actually a below grade (and the WT) "basement wall" fixed at the base and pinned at the ground floor slab and spans between the two which are in the order of 14m.

So yep a huge wall with large base moment and huge shear!