Curved Reinforced Concrete Slab 1

[BONILL]

I have the following curved reinforced concrete slab supported on three sides (See attached). I am trying to find a way to design the slab without being overly conservative. What would be the best way to design it?

Thanks for your help.

 

[Teguci]

Design a collector beam (slab depth if shear allows) 2.3 m over in the up down direction and run your reinforcement to it. Cantilever out the extra curve area.

 

[BAretired]

The Hillerborg Strip Method is one way. Yield Line Analysis is another.

BA

 

[ishvaaag]

Principal stresses in FEM at faces, plus check of the deflections. 30 cm thick, for weak to ordinary loads as in dwellings, the ordinary square mesh of 12 mm rebar at 200 mm in both directions should be enough. Rim embedded in all edges; and some shear reinforcement quite likely as per code in the short side.

Note I have not included an edge load. Make your model for your case. Also, further care in support conditions at edges would be required if the structure showed to be more critical. On these ordinary proportions may not be necessary, but always welcome.

 

[BONILL]

Thanks. I have taken the FEM approach and used some hand methods to confirm.

 

[RFreund]

BA -

Is this the method you refer to?

http://www.amazon.com/Strip-Method-Design-Handbook-Hillerborg/dp/0419187405

Sounds interesting, however I don't do enough concrete design to justify the cost.

ishvaaag - nice.

EIT

 

[BAretired]

RFreund,

Yes, that is the one. The advantage of the Strip Method is that it provides a lower bound to the load the slab can carry whereas the Yield Line method provides an upper bound. It is a good idea to check by both methods to determine the difference between upper and lower bounds.

BA

 

[rapt]

RFruend,

Both methods work but both only provide a strength solution. You still need to look at crack control requireemnts separately and put reinforcement in areas where there will be tension.

 

[BAretired]

I agree with rapt about crack control. With this particular geometry, it might be a good idea to consider a waffle slab to reduce the dead load.

BA

 

[SteelPE]

RFrend,

Some concrete design books do an overview of the Strip Method. Depending on how old you are, you may be able to dig out some old text books and get a good overview of what you would need to do. One text book I have gives a 34 page overview.

 

[RFreund]

Thanks for the responses - I'll have to check my texts but they are not very old. They have some Yield line overview but there doesn't appear to be a stip method overview

So is the Direct Design Method and Equivilent frame method that the ACI uses for 2-way slabs based on the strip method (column strip, middle strip)?


Thanks again.

EIT

 

[BONILL]

Attached are four nonregular concrete slabs.

I modeled as shell elements using SAP2000.

Slab thickness = 0.25 m.
Live Load = 0.90 Ton/m2
Dead Load = 0.45 Ton/m2
Maximum service load deflections = 0.07"
Principal stresses for service loading <400psi
Steel area corresponds to min. steel ---- #4 @ 0.15M. ea. way.

Are these values reasonable?