Minimum reinforcement in slabs

[HenkaCarlsson]

I'm calculating a tank and I have tried to let Robot calculate the minimum reinforcement for me but it seems to me that the values are to high.

I have the reinforcement type with simple bending.

The pictures in the pdf show part of the bottom of the tank and its 700 mm of concrete C40/50 (fctm=3.5MPa) at most and the minimum reinforcement is 17.6 cm2/m.

If I use the formula AsMin = 0.26 * (fctm / fyk) * b * d I get app 12 cm2/m. (fi16 fyk=500MPa)

What is the explanation to this difference?

If I change the type to "bending+compression/tension" to concider normal forces in the slab I get over 80 cm2/m in minimum reinforcement in some areas.

Do you have any explanation to this?

[Artur.Kosakowski]

Please check the code provisions for max. allowed bar spacing.

http://forums.autodesk.com/t5/Robot-Structural-Analysis/Minimum-reinforcement-on-slabs/m-p/3729178

The minimal area of reinforcement for tension is usually defined by different formula tan the value for bending.

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[HenkaCarlsson]

Yes the maximum distance is 250 mm according to 9.3.1.1 (3) which is 4*2,01=8,04 cm2/m.

[Artur.Kosakowski]

Attach the file please.

[HenkaCarlsson]

Here is the file. (Without results because of the size)

[Artur.Kosakowski]

Try to set the steel grades and bar sizes in the reinforcement parameters labels assigned to panels.

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[HenkaCarlsson]

I did that in my model from the beginning. It must have lost that setting in some way.

The difference is that when I choose B500BT as reinforcement grade it says "plain" instead of "deformed". Maybe that's the problem?

[Artur.Kosakowski]

Check what is set in the database

[HenkaCarlsson]

When I choose B500BT in the "Plate and shell reinforcement type" it says "Plain" but according to the database it should be deformed.

[Artur.Kosakowski]

Please check if you have a local version of this database in C:\Users\username\AppData\Roaming\Autodesk\Structural\Common Data\Robot version number and delete or move it. 

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[HenkaCarlsson]

I moved it and now it is "deformed" both in the "type"-dialog and in the database.

I have investigated the result a little bit more and I find that the result of the minimum reinforcement is depending on if you check the "Reinforcement adjust" for cracking in the SLS tab of the "Plate and shell reinforcement type".

I can't find a description of that tab in the Robot-help.

If that setting is unchecked I get results that correspond with 9.2 and 9.3 in EC 1992-1-1.

But if I check it I get much more minimum reinforcement even if there are no cracks. I wonder if the program uses 7.3.2 in EC instead and calculates the effective area of the concrete tension zone regarding the stress distribution?

Or if not how is it done?

[Artur.Kosakowski]

I moved it and now it is "deformed" both in the "type"-dialog and in the database.

So you were using your local (edited) version of the database. Mystery solved  

I have investigated the result a little bit more and I find that the result of the minimum reinforcement is depending on if you check the "Reinforcement adjust" for cracking in the SLS tab of the "Plate and shell reinforcement type".

I wonder if the program uses 7.3.2 in EC 

Formula (7.1) from 7.3.2

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