Leaderboard

The important consideration is ductility (elongation)of the reinforcement after yielding. Therefore provided the Grade 75 or even 80 can achieve the same elongation as a Grade 40 or 60 bar then that is fine. In Japan they use Grade 100 bars for seismic frames! In other countries reinforcement is classified as Grade 500A, 500B & 500C. The former (500A) being cold worked bar used for smaller diameters, Grade 500B for the general case, and 500C being hot rolled has the higher ductility and elongation and thus will be used in seismic frames. The key is to look at the material characteristics of the reinforcement, country of manufacture etc and compare elongation after yielding. The more the elongation the better the reinforcement for SMRF. In terms of concrete grade, there is a minimum grade for structural concrete in all concrete codes. Concrete reinforcement bond stress is based on concrete compressive stress and tensile splitting stress. The higher grade concrete, the higher these stress values are, BUT with more cement, more heat of hydration, more cost there are other considerations. 3000psi is minimum grade of structural concrete - anything less than this value does not work for concrete frames, and less psi concrete is us. Hence this minimum figure is specified - you can use higher grade of concrete if you wish, not an issue. Engineering and commercial decisions need to be made in selection of concrete grade and also reinforcement grade for that matter.