Why is the sum of the loads different than the sum of support forces? What is the cause of it?


  • In most cases, these differences can be attributed to a lack of convergence . Increasing the number of iterations and increments in the calculation parameters and FE mesh settings should help (see Figure 1).
  • High jumps in stiffness result in numerical problems, which leads to errors in the results evaluation. In RSTAB, this is no major problem for a complete and analytical approach function. In RFEM, on the other hand, approximation approaches are used, which is more likely to prevent high stiffness changes.
  • In case of members with elastic foundations, it may happen that deviations may occur as well. If the members are not or only roughly divided, convergence problems occur. A practical solution is to select a 'finer' distribution of members in the FE mesh settings (see Figure 2).


Convergence Elastic foundations Stiffness change Difference loads support forces Difference loads support reaction

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RFEM Main Program
RFEM 5.xx

Main Program

Structural engineering software for finite element analysis (FEA) of planar and spatial structural systems consisting of plates, walls, shells, members (beams), solids and contact elements

Price of First License
3,540.00 USD
RSTAB Main Program
RSTAB 8.xx

Main Program

The structural engineering software for design of frame, beam and truss structures, performing linear and nonlinear calculations of internal forces, deformations, and support reactions

Price of First License
2,550.00 USD