8925x
001098
2015-08-31

Quadratic Combinations SRSS and CQC as "Equivalent Linear Combination"

The modal results of a response spectrum analysis are combined with quadratic combination rules, and in RF‑/DYNAM Pro, the SRSS and the CQC rules are available. The default setting modifies the quadratic expressions into equivalent linear combinations. The advantage of this option is that the corresponding internal forces keep their signs and are often much smaller, compared to the standard SRSS or CQC rules. The standard SRSS and CQC rules are on the conservative side and the "equivalent linear combinations" are recommended.

The applied formulas are shown in the figure. It gives a specific example of this option when the SRSS rule is applied. It also works for the CQC rule.

Quadratic combinations, also in the form of the equivalent linear combinations, are available in RFEM and RSTAB and can be applied to any result combination. A license for RF‑/DYNAM Pro is not essentially required.

The "equivalent linear combination" was first published by Prof. Katz in the German journal D‑A‑CH‑Mitteilungsblatt.


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