Advice on the calculation method Slab reinforcement

Grasshopper Karamba3D
1

Hello everyone.

I read on the karamba 3D site that you first have to do an Optimise Cross Section to define the height of a concrete slab or wall before doing an OptiReinforcement to determine the reinforcement areas.

" Since the latter is a simplification, one should assure a sufficient height of the concrete cross section by using the “Optimize Cross Section” -component first."

What I understand from the OptiCrossSection of a tile is that you can calculate the minimum thickness so that the utilisation rate does not exceed 1 or another defined value.
If you want to calculate the thickness of the slab you need, neglecting the tense areas (which could become dimensional), I was deliberately going to increase the ftc of the material, to make sure that the dimensioning was only done in the compressed areas.
I understand that these are elastic stress distributions, and that non-linear characteristics have not been taken into account in the design.

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1- In your opinion, would this method be appropriate?

Then I recover the thickness found and do an OptimizeReinforcement to find my reinforcement areas :

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2 -What do you think of this approach? Despite the fact that it does not take into account the redistribution of forces in the concrete. Can I consider that my utilization rates reflect (more or less) my limit compressive stresses in the concrete (after this second calculation )?

3 - I intend to use this method for walls. For slabs, it doesn’t seem appropriate.
Is there by any chance a way of defining the non-linear behaviour of concrete and the distribution of stresses in concrete as a function of reinforcement?
With Karamba’s tools? Or any ideas on how to do this?

JP text OptiShellReinf_I.gh (78.8 KB)

(I have attached the gh file)

Regards

2

Hello @keuj.84,

ad 1.) For reinforced concrete design in karamba3D V2 one needs to manipulate the tensile strength of the concrete material to take account of the fact that the tensile stresses are covered by the reinforcement - otherwise the cross section optimizer would return too large cross sections which are governed by the small tensile strength of plain concrete. Your approach of setting the concrete tensile strength to a very large value can lead to large amounts of reinforcement in the reinforcement design step when bending moments dominate. In the example you attached, in-plane forces govern the design though and your procedure is fine.

ad 2.) The reinforcement optimization in K3D 2 does not check for crushed concrete and does not add compression reinforcement. In your case the concrete compression strength is fully utilized in the linear elastic calculation. When the tension zone cracks the zero-strain line will in reality move towards the compressed region where plastic deformations will take place. In your case I would thus suggest to reduce the the target utilization or the concrete compressive strength to take account of that. To arrive at a safe design it is necessary that the reinforcement yields before the concrete is crushed so that failure does not occur without prior warning like visible cracks and deformation. In addition to this make sure to include imperfections which may result from geometric errors, creep and second order theory.

ad 3.) In Karamba3D version 2 only linear elastic material behavior is accounted for. You could try out INCA2 (INCA2-Download) and Stab2D (Stab2D-NL - Download) for nonlinear RC calculations.

– Clemens

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