Flexural ductility of reinforced and prestressed concrete beams with maximum reinforcement ratios

To examine the flexural behavior of reinforced concrete beams with maximum reinforcement ratio, several reinforced concrete sections with different rebars are designed and analyzed using OpenSees. It was found that, although reasonable for rebars with yield point, the determination of the relative depth of the rectangular stress block for balanced failure given in the Chinese Concrete Code (GB50010-2010) is somewhat small for rebars without yield point. Based on the American Concrete Code (ACI318-19) and the work of previous scholars, this paper proposes a more accurate calculation method for the relative depth of the rectangular stress block for balanced failure based on the requirement of a conservative bearing capacity, and further extends it to prestressed medium strength rebars. Two reinforced concrete beams and one prestressed concrete beam were designed and tested with the proposed maximum reinforcement ratios. The outcomes demonstrate the validity of the proposed formula.