Stability design of single angle member using effective stress-strain method

Abstract

Single angle members are widely used in transmission line towers due to light weight and easy installation. However, angle members may experience complex behaviors such as flexural, flexural-torsional or lateral-torsional buckling due to unsymmetrical section and eccentric loading. The current design practice is generally based on the effective length method, in which semi-empirical formulas should be used to account for the actual end conditions and member initial imperfections. In contrast, advanced beam-column elements or finite shell elements should be used when using second-order direct analysis method without the need of effective length assumption. Direct model of the failure modes (i.e. local and global failure modes) of angle members is still a challenging task. This paper firstly investigates the sensitivity of the flexural-torsional buckling of eccentrically loaded members compared to the assumed flexural buckling mode about the principal minor axis which is implemented in most of available beam-column elements. Moreover, an effective stress-strain relationship representing the typical failure modes and initial imperfections, which has been calibrated by extensive finite element analysis and experimental results, is developed for the direct analysis of steel structures made of angle sections without use of the effective length method. The proposed method is so simple that it can be incorporated into any conventional beam-column elements to implement the direct analysis of angle structures. The examples show that the proposed method is sufficiently accurate and therefore it can be employed in the practical design of angle structures.