The ACI 318 Code (ACI 2011) combines the standard 45° truss model with an empirical concrete contribution to compensate for the conservative nature of this method. Alternatively, a variable-angle truss model plasticity has been developed on the basis of the lower bound theory of plasticity (Thürlimann 1979; Nielsen 1984) and is incorporated into the current Eurocode 2 [CEN 1992-1-1 (CEN 2005)]