Required reinforcement in slabs - funny results

[mathias_peron]

Hi, as I am using robot to design a reservoir, I get funny results for required reinforcement in slabs.

Robot doesn't seem to take into account cracking when performing the calculations. See below, for a 1000mm thick slab it gives me a max reinforcement equal to 703.59 mm2 at the peak. However when checking the forces at this particular point under worst SLS combination and I have a bending moment equal to 214.80 kN.m/m and almost no tension / compression. When doing the calcs by hand I get a way higher value!

Reinforcement required according to Robot

Reinforcement required

Axial force under SLS

Axial force under SLS

Bending under SLS

Bending moment under SLS

I think I have correctly set the parameters.

Can someone help me please? Artur?

Regards,

Mathias.

[Romanich]

Hi @mathias_peron ,

Could you share the model and hand calculations?

[mathias_peron]

Hi Romanich and thank you for your help.

Please find model and handcalcs here (too big for the forum) : https://we.tl/t-aoVJ89dKTq

This is for panel 15 at node 13996. Only the panels 'TH1000 (base)' seem to have this problem.

I hope you find the problem.

Regards,

Mathias.

[rsousa_ · Accepted solution]

Hi, 

did you notice that you don't have the minimum ammount of reinforcement as defined in EN1992-1-1? and that your moment is less that half of the cracking moment and maybe even at ULS your section isn't cracked at all?

But i can share my experience with cracking calculations in RSA:  i always do my checks by hand. Eurocode formulas are mainly for bending and have a lot of know problems (search Professor Beeby’s in structural concrete magazine) and you should see them as a good "quality" estimator. Putting this type of formula in a numerical algorithm is a nonsense in my humble opinion. But this is another subject that I'm sure other colleagues can share their opinions.

Regards

[mathias_peron]

Thanks rsousa!

No I didn't notice the section wasn't cracked, thanks for making me aware about this. Yes I deactivated minimum reinforcement to check my crack widths hand calcs.

Thank you again 😉

Regards,

Mathias.