Reinforcement for walls

[ByrnePM]

I have a general question relating to designing reinforcement for walls.

I have assigned the walls of my structure as “structural object = panel” and I am then designing the same way as slab panels,

with the exception that I am using the Analytical Approach for designing the required reinforcement (I use Equivalent W&A Moments for Slabs) as the axial load is high in the walls.

My query is, which forces should I be using to verify the proposed reinforcement sizes generated in Robot when using the analytical method?

I am getting some high required rebar sizes yet when examining the detailed moments and axial forces in the wall they all seem quite small?

When designing the slabs previously I have been able to check the Equivalent moments using the Complex Tab in the Map Results and do some hand calculations to verify Robot proposed sizes and this worked quite nicely

[Artur.Kosakowski]

Please check http://help.autodesk.com/cloudhelp/2016/ENU/Robot/files/GUID-E35C9B00-D485-4FD3-9988-6909AF7BC9D0.ht... 

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[Anonymous]

Hi Artur,

Apologies for resurrecting an old thread but I am also interested in this topic.

When using the analytical method for calculating required reinforcement how do I verify the internal forces used?

I am able to do this by using the complex tab in maps for panels - wood&armer but unsure of the approach for the analytical method.

I have tried the link if the previous post by it is not functioning.

Kind regards,

Dane

[Artur.Kosakowski]

This method by its principle doesn't have what you would name a single set of internal forces. Imagine a following approach:

You assume certain area of reinforcement in X and Y direction. Then you check if these areas are sufficient enough for internal forces on the X reinforcement direction and you repeat this check for internal forces changed by 12 degrees and you go on full circle optimizing amount of reinforcement for X and Y direction in such a way that the total area of reinforcement is the smallest possible. 

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[Anonymous]

Thank you for the response Artur.

I have read through the help file on the analytical method and your explanation above helps. 

From the help file I see that ɸ(Mn,Nn) is the reinforcement required to carry the internal forces calculated in direction "n". 

The forces in the direction "n" are calculated for increments of 12 degress using the transformation equations given in the help file.

I am struggling to understand why reinforcement values have to be assumed and then compared to already calculated required reinforcement values ɸ(Mn,Nn)?

Is this because ɸ(Mn,Nn) does not provide any information of reinforcement in each direction x and y therefore combinations of reinforcement x and y must be assummed such that ɸ(Mn,Nn) is achieved?

Thank you for taking the time to explain.

[Artur.Kosakowski]

You can determine a set of internal forces acting in the given direction of reinforcement and calculate requited area of reinforcement for this direction but it would be rather difficult to use this approach if the direction of forces which doesn't correspond to the direction of reinforcement 

It is easier to initially assume certain values of reinforcement for the directions that are not parallel to the direction of the internal forces and then verify the capacity of the slab. In this way you can increase or decrease Ax and AY running iterations intended to obtain such values that AX + AY is the minimal possible area but each of them is large enough to secure slab resistance for each of internal forces directions. 

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[Anonymous]

Okay so let me see if I understand correctly.

What we are essentially doing is calculating the required ɸ(Mn,Nn) for the slab throughout 360 degrees of transformation at 12 degree increments.

We then assume reinforcement amounts in the direction Ax and Ay. An is then similarly calculated throughout 360 degrees of transformation at 12 degree increments.

The transformation of the forces throughout 360 degrees creates an envelope of arbitary reinforcement quantities ɸ(Mn,Nn) for which each value of An throughout 360 degrees must be greater or equal.

Iterations on Ax and Ay are done such that the smallest sum of Ax + Ay is acheived whilst still being larger than ɸ(Mn,Nn).

[Artur.Kosakowski · Accepted solution]

Method of calculating plate and shell reinforcement - analytical method

You assume initial values of AX and AY. Then you calculate the equivalent area of reinforcement for n direction which corresponds to the direction of internal forces. You iterate AX and AY to have their sum being the lower possible value but these AX and AY areas have to be sufficient for internal forces transformed to all these (n) directions.

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[Anonymous]

Thank you Artur,

I think I understand.

I have attached a model and spreadsheet to try and do a check of my understanding.

Model is a simple beam modelled as shell with point load at midspan. I have extracted the Nx, Nxy and Ny from the most extreme element at the location of max moment.

I then created a spreadsheet according to what I understand the procedure is and checked if the reinforcement provided by Robot produced unity (ɸ(Nn)/An <= 1).

Please confirm whether my understanding is correct or not.

Regards

[Artur.Kosakowski]

I'm sorry for not answering earlier but I wanted to reach to the references which describe the algorithm of the analytical method. 

http://www.code-aster.org/doc/v12/fr/man_v/v3/v3.03.135.pdf

https://educnet.enpc.fr/pluginfile.php/16191/mod_resource/content/0/Coq_ELU_B.pdf

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