Critical Load Factor of Tapered Steel Frame 1: Eigenvalue Solver
Tips & Tricks
In the following example, the stability analysis of a steel frame can be performed according to the General Method in compliance with EN 1993‑1‑1, Cl. 6.3.4 in the RF‑/STEEL EC3 add‑on module. The first of my three posts shows the determination of the critical load factor for design loads required by the design concept, which reaches the elastic critical buckling load with deformations from the main framework plane.
A frame truss is loaded by a uniform load of 17.5 kN/m (on the top flange). You can specify the load application point in Details (“top flange, destabilizing effect” by default).
Boundary conditions of the separated substructure are defined in Window 1.6 of the RF‑/STEEL EC3 add‑on module. You can then start the calculation.
In this model, the critical load factor αcr of 2.376 results (see Figure). You can display the mode shape graphically in a new window for checking and evaluation purposes. The governing stability problem comprises the lateral-torsional buckling of the frame truss.
In the second post, the mode shape and the critical load factor will be calculated on a member model using the RF‑/FE‑LTB add‑on module.
In the third and last post, the mode shapes and the critical load factors determined previously will be evaluated using an FE model (surface elements) and the RF‑STABILITY add‑on module.
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