The ACI 2008 code permits the extensive use of higher strength reinforcements of up to 80,000 psi or 550 MPA.
One of the most notable developments since the 2002 edition is that the code recognizes only factored methods of design or the Ultimate Strength Design (USD) method. Earlier versions of the code permitted Working Stress Designs (WSD) along with the USD method.
Another development to be noted is in the USD design method, the code assigns a tensile strain value of 0.005 to the reinforcement in place of the 60,000 psi stress in older USD method of design, along with earlier 0.003 compressive strains in concrete. This clears the way for the use of steel of higher grade than Gr-60 in designing structures.
The code reflects the enhanced capability of concrete and re-bars producers in most parts of the world to manufacture a product to closer tolerances and specifications.
Another significant fact is that the ACI 2008 code claims to satisfy ISO 19338 “Performance and Assessment Requirements for Design Standards on Structural Concrete”.