This paper represents an extension of authors contribution [1] to the second order theory for thin-walled member with the open cross section. The presented theory differs form the conventional form by a unique treatment which includes the relations between the bimoment, St. Venant’s torque,, warping torque and other internal forces. The system of six scalar equations and an additional equation relating the deplanation of cross section are derived applying the principle of virtual work to the deformed confiquration of the member.