Unified Theory of Concrete Structures develops an integrated theory encompassing the various stress states experienced by RC structures under the various loading conditions of bending, axial load, shear, and torsion. Upon synthesis, the new rational theories replace the many empirical formulas currently used for shear, torsion, and membrane stress. The unified theory is divided into six model components: a) the struts-and-ties model, b) the equilibrium (plasticity) truss model, c) the Bernoulli compatibility truss model, d) the Mohr compatibility truss model, e) the softened truss model, and f) the softened membrane model.