The first order variation of critical loads of thin-walled columns with bisymmetric open cross-section due to some variations of the stiffness and location of bracing elements is derived. The considerations are based on the classical linear theory of thin-walled beams with non-deformable cross-section introduced by Vlasov . Both lateral braces and braces that restraint warping and torsion of the cross-section have been taken into account. In the numerical examples dealing with I-column, the functions describing the influence of location of the braces with unit stiffness on the critical load of torsional and flexural buckling are derived. The linear approximation of the exact relation of the critical load due to the variation of the stiffness and location of braces is determined.
17. C. Szymczak Torsional buckling of thin-walled beams of bisymmetric open cross-section [in Polish] Engineering Transactions 26 2 323-330 1978.
18. B. Gosowski Statecznosc przestrzenna stezonych podłuznie i poprzecznie pełnosciennych elementów konstrukcji metalowych [in Polish] Prace Naukowe Instytutu Budownictwa Politechniki Wrocławskiej Nr 66 Monografie 29 Wrocław 1992.