• sizi
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  • Registered: 2020-09-02
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Topic: modelling approach one-way slab

For my master thesis I am modelling a part of a continious slab system in order to specify the additional load carrying capacity by arching action.

I have several questions regarding this topic

1) First of all ragarding the modelling approach. As for one-way spanning slab a 2D moddeling approach over the height is appropiate, I wonder where the difference lies between the approach of using the material concrete and reinforcement for discrete bars and afterwards quadrilateral elements or using the 2D shell material (and discrete bars)?

2) At the beginning I am trying to model experimental tests from the literature to obtain some comparison possibilities. In some these not only the horizontal displacement was restraint but also the ends of the testing slab were fixed ends which means that the rotation was blocked. Within "define boundary conditions" there is the "rotation constraint for point/line" option, which is only applicable to 2D Shell or 1D beam elements. If I dont use the 2D shell material/element how can I block the roatation of the vertical line representing the height of my slab? Is it enough to block the hoirzontal displacement of the top and bottom ?
In addition I need to model a spring (horizontal displacement) in order to consider a neighbourfield (either point spring or line spring... depending on the results)
Are the conditions concering the same line for rotation and spring compatible?

Thank you in advance for your help!

Quote Post 1

  • dpryl
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Re: modelling approach one-way slab

Dear sizi,
ad 1.: I assume you have already read the corresponding manual section about Shell elements (ATENA 3D User's, 3.7.2.2.7 Shell Macroelements or ATENA-GiD User's, 5.3.2 Shell Material).

The main criteria against shell elements is if out-of-plane shear is expected to be important.

With respect to embedding discrete 1D bars in 2D shells, I suspect ATENA does not support this yet... which means you have to represent the bars as a smeared reinforcement layer (see also Troubleshooting, 2.2.6.1 Reinforcement layers in Shells).


Ad 2.: If you seek advice on modelling some particular support, please send us some sketches/photos along with a description illustrating the real setup (Troubleshooting, 2.1.1).

Above all, is the axial displacement blocked, or not (i.e., just the rotation and vertical displacement are blocked, but free horizontal sliding remains possible)? Or something else?

If you block horizontal displacement at a vertical surface, its rotation about a horizontal axis (e.g., edge of the surface) is prevented, too.

As I understand you are modelling one span of a continuous slab, possibly the best would be a periodic condition connecting the vertical surfaces at its 2 ends - if simply applying symmetry support at both ends (blocking displacements perpendicular to the surface) does not work well enough.

Or is the loading not periodic (the same for all spans)?


Regards.

dpryl's Website

Quote Post 2

  • sizi
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Re: modelling approach one-way slab

Dear dpryl,

thanks for your fast reply!

ragarding 2) the horizontal displacement is restrained. In the "theory" its not fully blocked but depends on the translatational stiffness of the neighbour field. For this reason my intention was to modell either a spring for a point at the vertical line representing the height of the slab(location is still unclear or could be investigated through a parametric study) or with a spirng for a line for the vertical line.

one can assume an equal distributed load for the continous slab system and therefore a periodic loading. How do you model a periodic connection though? Can you connect an periodic connection with a spring condition?

moreover it is recommended to use the symmetry of a model. therefore it would be enough to model the half of an inner field of a continous slab system. Meaning the periodic connection is only needed for one side?

Thank you in advance for your help

Kind regards

Quote Post 3

  • sizi
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Re: modelling approach one-way slab

I´m adding another question about the moddeling of springs.
There are 2 possibilities

1) one can assign spring for point or line through boundary conditions

2) one can assign a spring through materials

I read that it is recommended to use a special layer of line elements with spring material and that the spring for... condition is only availabe for backward compatibility.

Do I need to consider some extra things when I am using the spring material instead of spring condition? What does the sentece "a special layer of line elements" mean? Do I have to create a seperate layer with a line which gets the spring material assigned? Or can I just assign the spring material to a line of the surface which is part of the beam layer?

What does "backward" compatibility mean?

Thanks in advance!

Quote Post 4

  • Registered: 2020-09-07
  • Posts: 48

Re: modelling approach one-way slab

Hello Sizi,

you can use the boundary of surfae
- add special layer of line elements.. it means line and add the spring material for it, and master slave connect to surface
- backward compatiblity means, that in old examples was used the conditions... and if you delete it, the old examples will not work
but now, you can use both possibilities. The conditions have one advanced thing.. that you can choose normal of surface direction

Regards,
Mohamad

Quote Post 5