Question:
I would like to calculate the effective lengths for a frame column in the frame plane using RSBUCK or RF‑STABILITY. Which load case or load combination should I apply?
Answer:
RF‑STABILITY and RSBUCK perform an eigenvalue analysis for the entire model with a certain state of the axial force. Depending on the required number of eigenvalues, the results show the critical load factors with the corresponding buckling curves, and the effective length about the major and the minor axis for each member, depending on the mode shape. Since every load case usually has a different axial force state in the elements, a separate corresponding effective length result for the frame column is obtained for each load situation. The effective length whose buckling mode causes the column to buckle in the corresponding plane is the correct length for the design of the respective load situation. Since this result may be different for each design due to the different load situations, the longest effective length of all calculated analyses is assumed as equal for all load situations.
