Retaining Wall Keyway

[FEM4Structures]

Looking for information on keyway resistance capacity in retaining walls to resist shear.
30 ft high RC R/W with berm height of 22’-0”. Anticipated shear load at footing is 25 kips. Contractor intend to use keyway at footing level. Trying to size the keyway which can resist the shear at joint location. Insight or experience appreciated.


Thanks,

FEM4Structures

 

[jayrod12]

Are we talking a key for the wall into the footing or the footing into the soil?

 

[AELLC]

wall to footing = keyway

footing into the soil = soil key

 

[cvg]

key at the construction joint is unnecessary, and has been eliminated on many standard details - for instance Caltrans retaining walls have no key.

 

[AELLC]

Isn't a keyway necessary on some of the taller CMU walls?

 

[XR250]

I would imagine there would be enough friction to resist the wall sliding. The compressive force at the toe of the wall is likely to be huge.

 

[AELLC]

Also footing into soil = lug

 

[ztengguy]

Just check how much concrete you will need to resist 25 kip. Not a difficult calc. Also can use shear friction if you want.

 

[CBSE]

I use keyways on a lot of waste-water treatment tanks.

But yes, simple shear calc.

 

[FixedEarth]

See attached page from NAVFAC DM 7.2.

http://www.soilstructure.com/

 

[PilebuckEngineer]

Typical in my type of work (heavy highway, bridge) is 1/4" roughened surface or 1/3 the area if you want a keyway. Either way, no big deal and it's in most City or State standard specs.

 

[dik]

I seem to recall there was information by Fergusson (sp?) about 40 years ago that concrete in direct shear (not diagonal tension) for short stubby shear spans was in the order of 200 to 400 psi with the higher values for shorter stubbier shear spans. It was in one of his texts explaining why the loading within d of the support was neglected with a disclaimer that high loadings should be examined specifically.

Dik

 

[AELLC]

dik,

I have a 1973 textbook of his right here. ($17.50, can you believe that)

Reinforced Concrete Fundamentals.

 

[dik]

Can you check to see if there's a mention of concrete shear? Likely a different edition... mine would have dated about 1965, give or take... first text we had with Limit States Design or USD as it was known.

Dik

 

[AELLC]

dik - I will

By any chance do you have that funny essay by Russell Fling, where he compares concrete beam design by ASD to USD, saying USD is nonsense?

 

[FEM4Structures]

ACI Section 11.6.4 talks about Shear Friction Method.

Shear Reinforcement, Avf = Vu /[ (Phi=0.9)*Fy * (Shear Resistance = 0.6 for concrete)]


Calculate the reinforcement size required per lineal ft and provide a bar shared between footing and the stem with standard hook both end. Did anyone has experience using this method.


Thanks,

FEM4Structures

 

[AELLC]

FEM, so many years ago, I forget.

I used to do concrete (a long time ago) - then it was all steel - now all wood. grrrr.

 

[TXStructural]

Roughen the cold joint to 1/4-1/2 inch amplitude (this number is arbitrary, but should probably be less than half the large aggregate size.) Shear friction in engaged by the D- and O-bars (longitudinal and diagonal stem bars which develop in the stem and footing.) The D-bars also provide direct shear resistance as they are inclined to be in tension from both shear and flexure. Formed keys break off under load and you end up with the same kind of resistance as with a roughened joint, however, the roughened joint can easily extend across the entire interface.

 

[AELLC]

Shear-Friction. First scan.

The definition of a structural engineer: overdesign by a factor of 1.999, instead of the usual 2.

 

[AELLC]

Shear-Friction. Second (and last) scan.

The definition of a structural engineer: overdesign by a factor of 1.999, instead of the usual 2.