No backspan 6 ft long concrete cantilever

[sengineering]

I'm designing a 6 ft long (from CL of the wall) concrete cantilever with no backspan on top of a 16 in wide wall. This is the first time I'm designing a concrete cantilever, can you tell me what should be considered? Should i design a simple slab? What should I consider for the rebars since there is no backspan? The only load is live load.

(The cantilever is going to sit on 17 ft of the wall and span out 6.5 ft)

 

[rapt]

Hopefully it is not "sitting" on the wall! Or it will not for very long!

The Wall is the backspan. The moments must be developed back into the wall and down to the ground. Deflections will be caused by the cantilever deflection plus the rotation at the top of the wall.

This is a simply engineering problem, you should not be asking about it here if you have been tasked with designing it by someone who thinks you should know how it works.

 

[dik]

It appears that you have a 6' cantilevered slab sitting on the top of a 16" wall that is 17' high. Is there any lateral loading on the wall (soil other than any wind or seismic loading). the moment from the eccentric slab will have to be transferred directly to the footing. Is there any lateral restraint at the top of the wall?

Other than that, it's a relatively simple design problem... good luck with it.

Dik

 

[BAretired]

I think you should be concerned with the anchorage of the tension steel where bars turn the corner. There is a tendency for bars to develop high bearing stress immediately outside the bend, so you will probably want a substantial continuous transverse anchor bar under the bars near the bend.

BA

 

[sengineering]

Thanks for the answers.

This is going to be a wastewater aeration basin. So there is waste water behind the wall & it has no lateral resistance. Deflection wise it seems ok. I'm concerned about detailing of Steel, tension, and if there are any special considerations that I may be missing or if there are bites I should add to the drawings.

 

[apsix]

A generously sized fillet at the wall-slab junction will help detailing of the joint.
16" doesn't seem overly generous if the wall is cantilevering, hopefully it can also span horizontally.

 

[MotorCity]

I would design it as a tapered cantilever. The design of the cantilever is pretty straight forward, I would be more concerned with the effects it has on the basin wall. Since it is a liquid retaining structure, you will need to increase the moment and shear at the top of the wall by a pretty substantial factor according to the ACI (530??) code for environmental structures if you are in the US. If the basin is existing and you are adding the cantilever, that suggests post installed rebar anchoring....a whole lot more to consider