Leif Otto Nielsen

Limit Analysis of 3D Reinforced Concrete Beam Elements

A new finite-element framework for lower-bound limit analysis of reinforced concrete beams, subjected to loading in three dimensions, is presented. The method circumvents the need for a direct formulation of a complex section-force-based yield criterion by creating a discrete representation of the internal stress-state in the beam. The yield criteria are formulated and applied on a stress-state level. The stress-state is decomposed to concrete and reinforcement stresses, and separate yield criteria are applied to each component. Simple limits are used on the reinforcement stresses, and a modified Coulomb criterion is applied to the concrete stresses. The modified Coulomb criterion is approximated using second-order cone programming for improved performance over implementations using semidefinite programming. The element is verified by comparing the numerical results with analytical solutions.

Partly Cracked XFEM Interface for Intersecting Cracks

Throughout the last century intense research has been carried out regarding methods to determine the ultimate strength of reinforced concrete structures. Today well documented methods are available for estimating the ultimate strength of most reinforced concrete structures, however, most of these methods requires the use of empirical factors and do not consider phenomena such as size effects and reinforcement arrangement in detail.