For simply supported beams and girders of the span L where no lateral restraint to the compression flange is provided but each end of the beam is restrained against torsion, the effective LLT for the lateral torsional buckling is given in Table The effective length LLT for lateral torsional buckling of simply supported beams
Where, (D - overall depth of beam, L - length of span) Hence, the effective length of lateral buckling for a simply supported beam under normal loading conditions, provided torsional restraint as fully restrained and warping restraint as both flanges fully restrained should be 0.7L.