In this paper two different modelling techniques are presented and applied to nonlinear analysis of concrete structures considering B-regions and D-regions. A cross-section model capable of considering 3D phenomena and stress-states at the cross-section level is shown and applied to simulate complex load conditions considering torsion, shear, confinement, etc. The model is accurate both in service and ultimate condition and is based on mechanical considerations. On the other hand, a model to assist the design of D-regions and propose strut-and-tie (SAT) schemes capable of considering some constructability aspects is also presented. Performance of D-regions design according to different SAT schemes is assessed through nonlinear analysis both in service and ultimate situations.