Best way to analyse a L shaped slab

[ztengguy]

I have been asked to look at a flat slab in a L shape configuration on its side, 8' wide, with 1.5' downward return. All sections 6" thick. Whats the best way to analyze this, Do you consider the whole slab stiffened by the return, or do you look only at a certain width stiffened? I am worried about deflection at the edge that does not have a return.
Thanks

 

[CELinOttawa]

This depends a great deal on the support arrangement...

Generally I would analyse as an unstiffened slab to do the bars throughout, the look at any additional load attracted by the stiffening effect of the downturn and ensure I addressed it.

Keep it simple; The answer needs reliable load paths, as well as sufficient strength and stiffness to be fit for purpose. It doesn't need to be a perfect solution or engineered to a hair's width precision, just safe and reliable without being wasteful.

 

[hokie66]

If it is only 6" thick, the span can't be great, so I would just ignore the beam on one edge and reinforce as a uniform depth slab. Whatever benefit is gained by the downturn is a bonus.

 

[ztengguy]

Its actually 22', a precaster is asking me if it can be done without prestressing.

 

[CELinOttawa]

My gut says no... I think you'll have a serious shear problem without prestressing at only 150mm thickness for a span like that... For 150mm thick you're usually topping out at 4m, for 22' you're talking more than 50% over the typical maximum!

Anyone else?

 

[hokie66]

Prestressed or not, I don't see how that can work for a precast slab section. Prestressing won't help very much in such a thin section.

 

[CELinOttawa]

Prestressed slabs are possible to a maximum ratio of L/50. At a span of 6.7m, 150mm can be made to work if prestressed.

 

[ztengguy]

Yea, I looked at it and decided that it would need some strands. Thanks