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RISA 3D vs STAAD PLATE RESULT

RISA 3D vs STAAD PLATE RESULT

RISA 3D vs STAAD PLATE RESULT

(OP)
I am trying to model a gorund bearing concrete pad . The model is composed of concrete plate elements. After analyzing the problem in STAAD Pro and RISA 3D, I obtain different plate forces and results do not match.

STAAD Pro and RISA 3D models are also attached in the zip files. The only dead load on the structure is plate load of 314 Kpa applied to all plates perpendicular to their plane.

I would like to believe that the results for a smaller problem as the one attached should match right on.

Question: Am i modeling incorrectly such the results are not the same?

RE: RISA 3D vs STAAD PLATE RESULT

What results are you trying to compare? Plate forces? Corner Forces? The two programs may have different ways of reporting results. I know RISA reports corner forces based on actual displacements but plate forces are per foot.

RE: RISA 3D vs STAAD PLATE RESULT

There are some differences between the two files. First is the material properties.

16602 vs 25124 MPa for E
7219 vs 10921 MPa for G
1762 vs 2323 kg/m^3 for Density

Then it is unclear to me what spring constant is actually being used for the soil springs in the STAAD model. In the RISA model, they are clearly compression only springs with a spring constant of 4.8267 kN/mm (for the interior joints). But, the STAAD model seems like it might be quite a bit softer than that (based on a subgrade modulus of 2778 kg/m^3). If I'm correct, that's a factor of approximately 150 between the soil spring stiffness in the two models.

Of course, I'm not 100% certain of the STAAD units for subgrade modulus or how they convert from subgrade modulus to spring constants. Because that's not something that the STAAD import feature of RISA-3D translates. But, my guess is that those two differences (material properties and soil springs) accounts for the majority of the differences between the two solutions.

Note:
RISA and STAAD plate results should not match exactly as they use different FEM plate formulations. But, for a well meshed model like this they should normally be pretty close.

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