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2024-05-29

FE Mesh Refinement Factor for Reducing Calculation Time

How can I reduce the calculation time for members with a nonlinear material model in RFEM 6 and RSTAB 9?


Answer:

In the case of the structural analysis of members with a nonlinear material model, an FE mesh is generated on the cross-sectional area and used for the calculation. As of the versions RFEM 6.06.0009 and RSTAB 6.06.0009, it is possible to adjust the mesh density for the FE mesh of the cross-sectional area via a refinement factor.

The preset mesh is relatively fine by default, and thus ensures a high degree of accuracy for the calculation results.
However, a coarser FE mesh may be completely sufficient in many cases, reducing the calculation time significantly.

You can adjust the FE mesh refinement factor in the "Edit Section" dialog box, the "FE Mesh" tab. The smaller the value, the finer the mesh.


The effects of the mesh density of the cross-sectional area on the calculation time and internal forces are shown below, using a simple example.

Cross-section: HD 260*54.1
Material: S235
Material model: Isotropic / Plastic (Members)
A vertical distributed load is applied over the entire length of the beam, and it is so large that a plastic hinge is formed above the central support.

Different FE mesh refinement factors between 0.5 and 5.8 will be analyzed. The calculation time as well as the support and sagging moment are evaluated. The relative deviation from the results with an FE mesh refinement factor of 1.0 is shown in brackets.

FE Mesh Refinement Factor Calculation Time Plastic Support Moment Sagging Moment
[-] [s] [kNm] [kNm]
0.5 (-50%) 99 (+175%) -174.12 (-0.08%) 122.4 (+0.05%)
0.75 (-25%) 53 (+47.22%) -174.17 (-0.05%) 122.38 (+0.03%)
1.00 36 -174.26 122.34
2.4 (+140%) 22 (-38.89%) -174.81 (+0.32%) 122.13 (-0.17%)
4 (+400%) 19 (-47.22%) -174.8 (+0.31%) 122.13 (-0.17%)
5.8 (+580%) 17 (-52.78%) -174.83 (+0.33%) 122.12 (-0.18%)

The table shows that it is reasonable to increase the FE mesh refinement factor for this structural system. In the case of relatively small deviations of internal forces (less than 1%), the calculation time for a structural analysis can be roughly halved.


Author

Mr. Wanke provides technical support for customers of Dlubal Software.