I am applying a uniform load of 15 kN/m on a 25 m simply supported I girder beam of certain dimensions. And I am unable to find critical buckling factors in SAP 2000.

The paper mentions that for the steel section beams, the critical load factor for lateral torsional buckling is calculated using a linear buckling analysis . For the critical load factors of the 1D model, beam elements with seven degrees of freedom were used.

Please find the attached files for errors and model representation.