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2015-10-29

Dynamic Combinations (SRSS as "Equivalent Linear Combination")

Result combinations exported from RF‑/DYNAM Pro – Equivalent Loads are generated by superimposing the results from the individual modal responses. For this, the SRSS rule can be used as "equivalent linear combination". When result combinations are used in RF‑/STEEL, two options are available for calculating stresses. In the first option, the results from the result combinations are used directly. This is done line by line, for each maximum and minimum controlling internal force. In the second option, stresses are determined from the individual load cases. The quadratic superposition rule is then performed again in RF-/STEEL.

The "equivalent linear combination", as used by RF‑/DYNAM Pro, is also considered by RF‑/STEEL. RF‑/STEEL calculates the governing internal forces. These are sometimes difficult to understand and not directly comparable with the result combinations themselves, for example when the equivalent stresses are used for calculating the governing internal forces, which is the default in RF‑/STEEL.

When you use the pure normal stresses or pure bending stresses for the calculation of governing internal forces in RF‑/STEEL, you can easily reproduce the resulting internal forces. You will see that the "equivalent linear combination" option is used by RF‑/STEEL.

The formulas and an example are provided in the image.




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