Abstract This paper extends the study made on determining the inelastic lateral torsional buckling strength of monosymmetric stepped I-beam in consideration of its degree of monosymmetry by making a destructive test while subjecting the beam to a concentrated load. Prior to the test, numerical values of the expected results are estimated by finite element analysis using the program ABAQUS. The numerical results are estimated by creating a model which experiences the same conditions as that of the test specimen. Then, a comparison is made with the experimental results, the results from the proposed equation and the results from the finite element analysis. In succession, the safety and economic feasibility of the proposed equation is evaluated. Finally, the comparisons made showed that the proposed equation yielded results that are acceptable and has values that are similar to the values yielded by the test. More tests are needed to determine if the proposed equation is also suitable for other loading conditions.