Buckling assessment of steel members through overall imperfection method

• A general imperfection method is developed to assess the buckling of members.
• Equivalent amplitude is derived to assess the lateral torsional buckling.
• An equivalent amplitude is proposed to assess the coupled buckling.
• Computer aided procedure of the method is developed.
• Benchmark examples were investigated to validate the proposed method.

This paper presents a proposal for an overall imperfection method utilizing Linear Buckling Analysis (LBA) and developed equivalent initial imperfection for the assessment of the out-of-plane buckling resistance of steel members. The equivalent initial imperfection for the flexural buckling assessment of columns subjected to compressive force has been specified in the Eurocode 3. In this paper this formula is reorganized in order to establish a suitable computer-aided procedure, and then the equivalent initial imperfection for the fundamental cases of lateral torsional buckling and coupled buckling are defined. (Fundamental case: simply-supported member with uniform cross-section subjected to uniformly distributed forces; the buckling resistance of this reference member has been defined by a standardized design equation based on theoretical and empirical background). The amplitude for the equivalent initial imperfection in the shape of the buckling mode is expressed with second-order normal stresses, on one hand calculated with the equivalent amplitude specified in the relevant standard (e.g. Eurocode 3), and on the other hand calculated with the initial imperfection in the shape of the buckling mode with arbitrary amplitude. The design formula derived for the fundamental case is generalized by the equivalent member concept. The stability assessment is carried out verifying the cross-section resistance of the designed member using second-order elastic analysis with the derived equivalent initial imperfection. The proposed overall imperfection method is adequate for computer-aided design methodology which is based on advanced elastic beam–column finite element method. The accuracy and practicality of the proposed method are illustrated for regular, irregular, single and multi-span members.