Efforts increasing in the destroyed finite elements of shell during the nonlinear analysis.

Hello. What may cause the increasing of efforts in the destroyed shell finite elements (in reinforced concrete floor structure) with nonlinear analysis? When the calculation of non-linear bar finite elements it doesn’t happen, the moment is equal to the limit value, which can be beared by the cross section. Why does it happen?

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Efforts increasing in the destroyed finite elements of shell during the nonlinear analysis.
 
#1
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Dec 12, 2016 14:30:59
Hello. What may cause the increasing of efforts in the destroyed shell finite elements (in reinforced concrete floor structure) with nonlinear analysis? When the calculation of non-linear bar finite elements it doesn’t happen, the moment is equal to the limit value, which can be beared by the cross section. Why does it happen?
 
 
 
#2
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Dec 14, 2016 15:56:22
Announce the software package version; the method by which you determined that the limit efforts were achieved (taking into account the efforts within two planes); Set the analytic model itself or a fragment, where this situation can be achieved, and perhaps the discussion will appear.
 
 
 
#3
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Dec 14, 2016 17:16:14
Version 2014 R4. As an exemple I considered a continuous beam (width is 1 m, bay is 6 m, height is 0.2 m. The upper and lower reinforcement is 5.2 cm2. Concrete is B25 and armature is A500. The load is uniformly distributed and is equal 1.22 t / m2. To compare the results I also made a bar  element with the same parameters and reinforcement.
Whithin the bar model everything is okay, first the support section destroyed then after a time the span section does.

In the plates scheme in 2014 version after the destruction of two FE near the support, the analysis stops and the span moment doesn’t achieve the beam bearing capability, then the load factor is smaller than in the scheme with bar FE.

In earlier versions, it was different. The analisys not stopped and the efforts in support finite elements continued to increase (not as much as before the destruction but still) and so on until the destruction of the span FE. And the limit load was greater than in  the bar model.

It turns out that the limit equilibrium method can’t be implemented in the shells cheme in 2014 R4, can it?  Or I do something wrong?
 
 
 
#4
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Jan 6, 2017 14:05:56
Please, show the files of materials state. I didn’t see any problems, there is a plastic hinge within the cross section of the bar and also within the cross section of the plates. So everything looks right. The numbers are not completely identical, but, conceptually, the same thing. The analysis stops because of appearance of the unstable structure, and what is the idea of doing like this? By the way, the approximation is not quite successful (1m width with a thickness of 20cm, it shoudn’t be neglected for plates), it’s also better to set your own deformation law (piecewise linear function), to continue to look for the difference between the results.

By the way (about the approximation), I made the plate slabs to work in accordance with the flat cross-section hypothesis - set perfectly rigid body in every section after what the analysis was end without problems. The plastic hinge formed in two rows of elements from the bearing section, it shows the redistribution, doesn’t it? There is only one plastic hinge within the bars. And why the analysis stops I I
 
 
 
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