Critical Load Factor
Tips & Tricks
RSTAB can calculate a critical load factor for each load case LC and each load combination CO in compliance with the second‑order analysis. The critical load factor indicates the number by which the load must be multiplied so that the model under the associated load becomes unstable (buckling).
The critical load factor is determined internally by a load increment. The load factor becomes the critical load factor, when the program finds no equilibrium in the deformed system for the existing loading condition according to the second‑order analysis (= becomes unstable).
In contrast to the solution of a buckling eigenvalue problem (such as in RSBUCK and RF‑STABILITY), this procedure helps you also consider other structural nonlinearities (for example support failures, member failures etc.) in an optimal way.
You can activate the calculation of the critical load factor for each load case and load combination in the ‘Calculation parameters’ tab. The iterative process itself requires an initial load factor and a load factor increment. In case the program cannot find the equilibrium for the load factor 1.0 anymore, and the initial load factor is < 1.0 (unstable), no result is given due to the lack of internal forces and deformations in the load step 1.0.
Since the calculation of the critical load factor can extremely increase the computation time due to the iterative approach, you should set this function only for the desired load situations (LC, CO).
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The structural engineering software for design of frame, beam and truss structures, performing linear and nonlinear calculations of internal forces, deformations, and support reactions