Elastic Critical Load (ECL) Analysis

Elastic Critical Load Analysis (also referred to as stability, or buckling analysis) computes the elastic critical load factor, lambda_c, for a structure subjected to a particular set of applied loads. This load factor is the ratio by which the axial forces in the members of the structure must be increased to cause the structure to become unstable due to the flexural buckling of one or more members (lateral torsional buckling of individual members is not taken into account). The elastic critical load of the structure is a function of the elastic properties of the structure and the pattern of loading.

Once the elastic critical load is known, member effective lengths can be calculated. The effective length of a member is defined as the length of an ideal pin-ended strut having the same elastic critical load as the load existing in the member when the structure is at its critical load. The effective length may be expressed as a factor multiplying the actual member length.

The effective length factor is calculated separately for each of the member principal axes for each load case. A load factor of less than 1.0 for any load case indicates that the structure is unstable under the applied loading.

The elastic critical load for any load case is determined by computing the axial forces in the members of the structure and then increasing them in proportion until the structure becomes unstable. At this point the factor by which the axial forces have been increased is the elastic critical load factor for the structure under the current loading. The elastic critical load factor is also known as the "buckling load factor" or the "frame buckling factor computed from a rational buckling analysis". You may specify the number of buckling modes to be computed (normally, only the first or lowest buckling mode is required). The mode shapes may then be displayed.