FAQ 002108 EN

Calculation RFEM RSTAB 5.xx 8.xx

When calculating a result combination, I receive the ‘Warning No. 30014 – Incorrect addition of load cases in the result combination! The result combination contains load cases or load combinations with results containing second‑order effects, which points towards nonlinear relationships and therefore cannot be added together...’ What does this warning mean?

Answer

This warning appears in the case of the following result combination definitions when the load cases/load combinations are analysed according to a nonlinear analysis such as second‑order or large deformation analysis.

Case 1: RC = LC1/CO1 + LC2/CO2

For Case 1, load cases/load combinations cannot be superimposed together in a result combination when each case/combination is ran according to a nonlinear analysis such as a second‑order (P‑Delta, p‑delta) or large deformation analysis. Deformations in both load cases are based on different structural systems and will result in incorrect results as P‑Delta effects cannot be simply added together.

The solution for this case is to either run the load cases/load combinations according to a geometrically linear analysis where the results can be superimposed together in a result combination, or the consideration of the combined load cases must only be considered under the Load Combinations tab and evaluated individually rather than in a result combination.

Keep in mind, this same warning will appear when creating a result combination in a model where geometric nonlinearities are also defined. An example includes a slab foundation where a nonlinear surface support is defined to fail in the case of uplift. Geometric nonlinearities can accurately be considered in load combinations opposed to result combinations which may yield incorrect summary results.

Case 2: RC = factor* LC1/CO1 or factor* LC2/CO2

For Case 2, if a load case/load combination is calculated according to a nonlinear analysis, it is not possible to additionally apply a factor to the result combination. The factor would not only be applied to the defined loads on the structure, but also to the nonlinear effects such as P‑Delta which is incorrect.

The solution for this case is to either run the load cases/load combinations according to a geometrically linear analysis where the factor can be applied to the result combination, or the factor can be considered under the Load Combinations tab where it will be applied directly to load cases only according to a geometrically linear analysis without consideration to the second‑order effects.

Keywords

load case, load combination, result combination, warning, incorrect, addition, second-order analysis

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

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