A full 3D cross-section model is described and used to evaluate the performance of concrete columns. By means of a particular functional equation which ensures internal equilibrium among fibres, and the consideration for warping and distortion, the model is capable of taking into account the 3D phenomena involved in biaxial shear loading and confinement of concrete structures. Case studies are analysed to demonstrate these capabilities involving shear, confinement and distribution of transverse reinforcement. Latter, the performance of poorly detailed concrete columns failing in shear or retrofitted by external FRP.