Displacement and mixed fibre beam elements for modelling of slender reinforced concrete structures under cyclic loads

In this paper, two fibre-based beam elements with enhanced capabilities to consider large displacements and rotations of slender reinforced concrete members are developed. Fibre beam elements were comprehensively used before to model the behaviour of different structural systems with great accuracy. To upsurge the use of the fibre beam elements in modelling complex reinforced concrete (RC) systems such as slender walls and columns, the elements are improved by including the second order effect. Available research from the literature related to large displacements focused mainly on modelling steel and composite members due to the limitations in their material model behaviour. Conversely, the newly developed elements introduced in this paper can precisely model RC members by accounting for their more complex nonlinear material behaviour under reversed cyclic loads. The first element is formulated using a displacement formulation, while the second element is based on a mixed approach that is computationally more complicated but numerically more efficient. Further, the adopted concrete constitutive law accounts for the effect of compression post-peak softening as well as tension stiffening and degradation under cyclic loads. Several correlation studies are presented to highlight the efficiency of the new elements in modelling slender RC structures.