🕑 Reading time: 1 minuteReinforced concrete beams are classified as balanced, under-reinforced and over-reinforced based on percentage of reinforcement it has. Details of these beam sections are discussed.
Balanced, Under-Reinforced and Over-Reinforced Beam SectionsMoment of resistance of reinforced concrete beams are calculated based on following assumptions: 1. Plane sections remain plane in bending up to the point of failure. This means that strains are proportional to distance from the neural axis. 2. Ultimate limit state of bending failure is assumed to have been reached when the strain in the concrete at the extreme bending compression fiber reaches 0.0035.
Fig: Strain diagram of a beam section; (a) Section, (b) Strain diagram3. The stress distribution across compression face will correspond to the stress-strain diagram for concrete in compression. 4. The tensile strength of concrete is neglected as the section is assumed to be cracked up to the neutral axis. 5. The stress in steel will correspond to the corresponding strain in the steel. As given in assumption 2 above that the reinforced concrete section in bending is assumed to fail when the compression strain in concrete reaches the failure strain in bending compression equal to 0.0035.
Balanced Beam SectionReinforced concrete beam sections in which the tension steel also reaches yield strain simultaneously as the concrete reaches the failure strain in bending are called balanced sections.