Check reinforcement calculation concrete plate

I like to make a calculation with XFEM4U, to calculate the reinforment. But it is the first time I will use this tool. So I have made exercise, a simple plate on two supports. M = 1/8ql2, you know.
XF have a good calculation. But I do not understand the calculation of the reinforcement.
XF gives 392 mm2/m1 and my own calculation gives 293 mm2/m1.
How is that possible? I have read the paragraph of Blaauwendraad, but thats not clear…
Its also my first on this site, I will try to use this facility. but in English…
I have to learn any more…

1 Like

Hi Leo,

Could you send me your input (xfem-file)? And also your calculation as well? We will response soon!

Hi Rob,
Here several docuyments:

  1. hand calculation
  2. XFEM4U and XConstruxt files.

betondoorsnede.xcst (5.4 KB)
plate excercise 29-10-2022.xfem (165.4 KB)
Plate excercise calculation.pdf (14.8 KB)
I hope you have enough information…!

Hi Leo,
Sorry for my late reply. I have looked at your calculation. In XFEM4U we use a ‘sandwich’ calculation method. See attached files. We assume a layer at the top and a layer at the bottom. In both layers the internal forces are calculated.
The initial layer thickness is now calculated by 2 x cover + reinforcement = 66 mm. This causes an internal lever arm of 180-66 =114mm. Please examine the attached file reinforcement_XFEM4U.pdf.
For thin plates at low bending loads this will give a higher amount of reinforcement.
Perhaps the initial layer thickness is too big here. I will ask Johan Blaauwendraad how to deal with this. Your helpdesk number is #1637
reinforcement_XFEM4U.pdf (139.1 KB)
Wapenen van schijven, platen en schalen, Versie 19-11-2019.pdf (843.9 KB)
Cement Online Artikel. 20-12-2021.pdf (653.0 KB)

Hi Leo,
After consulting Johan Blaauwendraad we have adjusted the initial layer thicknesses.
The starting values of the layer thicknesses are reduced so that the initial internal lever arm corresponds to 0.9d. For relatively thin and low loaded slabs, this significantly reduces the amount of longitudinal reinforcement required. When the height concrete pressure zone proves too small to absorb the concrete pressure force, the layer thickness is automatically increased in 1-mm increments. See attachments.

1637 met 43kNm2.xfem (165.5 KB)
1637 met grote belasting.pdf (141.3 KB)
1637.pdf (141.2 KB)
plate excercise 29-10-2022.xfem (165.4 KB)

1 Like

Thanks you very much Rob.
Regards, Leo