An efficient geometrically exact beam element for composite columns and its application to concrete encased steel I-sections

• A geometrically exact 2D beam element for composite columns is proposed and validated.
• The element is computationally efficient and complies with the principles of the general method of Eurocode 4.
• The buckling behaviour of concrete encased steel I-section columns is investigated.
• The influence of the equivalent member imperfections and the concrete material law is assessed.

In this paper, a computationally efficient geometrically exact and materially non-linear 2D Euler–Bernoulli beam finite element is proposed, which is capable of accurately capturing the buckling behaviour of steel–concrete composite columns and complies with the principles of the general method of Eurocode 4 (EC4) (EN 1994-1-1:2004, 2004). The element is easy to implement and, due to the Euler–Bernoulli constraint, only requires uniaxial material laws for both steel and concrete. The element is subsequently employed to investigate the buckling behaviour of partially and fully concrete encased steel I-section uniformly compressed columns. In particular, the results of a parametric study are presented and discussed, aiming at assessing the influence of the equivalent member imperfections and the concrete material law, in order to provide recommendations concerning their use in non-linear analysis according to the general method of EC4.