Corbel or Ledge? 1

[JackTrades]

I'm designing a sluice gate structure with a ledge(?) at the top of a deep reinforced concrete box. The ledge is about 20 feet long and will have two point loads occurring about 10 feet apart at the gate lift locations. My question concerns design method - should this be seen as a cantilever ledge or as two corbels? If designed as corbels, should I use the same closed stirrups as if they were isolated and not intrinsic to the continuous ledge?

Any direction or suggestions appreciated.

-Jack

 

[dik]

I would treat them as two corbels with the point loads. Can you do the corbel in structural steel as a 'bolt on'? Might be cheaper. Don't know the magnitude of the loads or the sizes required.

Dik

 

[WillisV]

Design it as a beam ledge - this is analogous to girder ledges used to support precase double-Ts. There is a design procedure outlined in PCA Notes on ACI 318-0X Building Code. For the -05 version see p15-3 and Example 15.3.

 

[dik]

Can we get a tie breaker?

Dik

 

[haynewp]

You should be able to design it either way. PCA notes have examples of each methood. I might look at it as 2 corbels ignoring the adjacent concrete and then as a beam ledge, then compare the cost of construction of each way to make the decision. But yes, I would include all the ties if I treated it like corbels.

If the loads are not high and you have the constant ledge anyway, then it might be cheaper to go with the constant depth beam ledge. Do you have a contractor on the project?

 

[haynewp]

If they make the ledge the same profile throughout, and they misplace the loads relative to where the corbel ties were installed (or vice versa) there could be a potential problem. The more foolproof way might be to use the beam ledge concept since the corbels may not be isolated as they usually are.

 

[JackTrades]

dik, willisV, and haynewp,

I can't use structural steel for the corbel as I'll need the full length C.I.P. concrete ledge for a working platform for maintenance.
The loads are about 30k each vertical with no applied Nu.
I have a copy of the PCA Notes on ACI 318-02 which has examples of both methods. Should have checked before posting.
I'm going to go with the ledge design.

Thanks to you all for your help.

-Jack

 

[WillisV]

Woohoo!