Dowels only for shear transfer

[jdonville]

Folks,

I have a project involving a short plain concrete wall on a plain concrete footing (ease of construction).

The wall and footing will (likely) be cast-in-place using slipform methods.

What is the formula for calculating the shear transfer provided by regularly-spaced dowels at the joint between the two elements (wall and footing) assuming that:

1) no special roughening is performed,
2) no key shape is cast into the top of the footing

The project is being designed in accordance with AASHTO HB-17/2002, if that helps.

It's been a long time since my college structural design courses, so please be nice and furnish a brief explanation of the nomenclature.

Thanks,

Jeff

 

[Lion06]

SEE ACI 318-05 Section 11.7 regarding shear friction.
Vn=Avf*fy*(coefficient of friction). Vn is the nominal shear resistance provided by your regularly spaced dowel, Avf is the area of your regularly spaced dowels (in in^2/ft), fy=the yield stress of your Reinforcing bars (60ksi), and I would use the coefficient of friction of 0.6 for concrete place against hardened concrete not intentionally roughened per 11.7.4.3.
Hope this helps.

 

[JLNJ]

I am curious as to what kind of wall you have - pure shear. A gravity retaining wall?

 

[miecz]

I figure this must be a trick question, so I'll bite

For the "Strength Design Method", this is covered by formula 8-46 of section 8.16.6.1.1.

Vu < phi x Vn

Vu is defined in 8.1.2 as the Factored shear force
phi is defined as 0.85 in 8.16.1.2.2
Vn is defined by formusl 8-56 in 8.16.6.4.4. as follows

Vn=Avf x fy x mu

Avf is defined in 8.1.2 as the area of shear friction reinforcement
fy is defined in 8.1.2 as the specified yield strenght of reinforcement
mu is defined in 8.16.6.4.4(c) as 0.6 x lambda, for concrete not intentionally roughened
lambda is definded in 8.16.6.4.4 as 1.0 for normal weight concrete

According to 8.16.6.4.5,
Vn < 0.2 x f`c x Acv and Vn < 800 x Acv

where Acv is the area of concrete resisting shear transfer.

 

[MHSpurs]

I'd say you could use 0.6pyAs similar to steel shear capacity.

 

[jdonville]

Thanks for the responses. I don't have the ACI code, so while your code references don't mean all that much to me, thanks for providing them just the same.

Naturally, I will have a structural designer prepare the final design, but I want to verify that my proposal will pass muster in advance.

Basically the wall will be a gravity retaining wall. Since the cheapest way to construct it will be slipforming as described above, I will need to transfer horizontal loads to the separately cast footing. The wall will need to provide lateral resistance in both directions, due to the possibility of traffic impact.

Jeff

 

[miecz]

My code references were to AASHTO HB-17/2002, as you requested.

 

[jdonville]

Whoops,

I do, in fact, have a copy of the ACI code available.

Jeff

 

[jdonville]

jmiec,

Much appreciated.

Jeff