The solution of impact problems requires advanced computational techniques to overcome the difficulties associated with large short-duration loads. In this case, the explicit time integration method is typically used, since it provides a stable solution for problems such as the analysis of structures subjected to shock and impact loads. However, most explicit-based finite elements were developed for continuum models such as membrane and solid elements, which renders the problem computationally expensive. On the other hand, the development of fiber-based beam finite elements allows for the simulation of the global structural behavior with very few degrees of freedoms, while accounting for the detailed material nonlinearity along the element length. However, explicit-based fiber beam elements have not been properly formulated, in particular for the case of the emerging force-based beam element. In this paper, two developed fiber plane beam elements that consider an explicit time integration scheme for the solution of the dynamic equation of motion are presented. The first element uses a displacement-based formulation, while the second element uses a force-based formulation. For the latter case, a new algorithm that eliminates the need for iterations at the element level is proposed. The developed elements require the use of a lumped mass matrix and a small time increment to ensure numerical stability. No iterations or convergence checks 2 are required, which renders the problem numerically efficient. The developed explicit fiber beam-column models, particularly the force-based element, represents a simple yet powerful tool for simulating the nonlinear complex effect of impact loads on structures accurately while using very few finite elements. The traditional implicit method of analysis typically fails to provide numerical stable behavior for such short time duration problems. Two correlation studies are presented to highlight the efficiency of the developed elements in modelling impact problems where the strain rate effect is considered in the material models. These examples confirm the accuracy and efficiency of the presented elements.

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 postpeak 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.

No abstract