👉Sections of Beam (Based on Reinforcement)

💫Reinforced concrete beams are classified into Balanced, Under-Reinforced, and Over-Reinforced sections based on the amount of steel provided.

🚧1) Balanced Section

▶️A balanced section is one in which both concrete and steel reach their permissible stresses at the same time.

• Concrete reaches its maximum compressive strain
• Steel just reaches its yield stress
• Neutral axis depth = critical depth

▶️Failure nature:

• Sudden and brittle

📜Remarks:

• Ideal theoretical condition
• Rarely used in practice due to lack of warning before failure

🚧2) Under-Reinforced Section

▶️An under-reinforced section has less steel than required for a balanced section.

• Steel yields first before concrete crushes
• Neutral axis depth < critical depth

📜Failure nature:

• Ductile failure
• Large deflection and visible cracks before failure

🎲Advantages:

• Gives sufficient warning before collapse
• Safe and preferred in design

🔰Used in practice:

• YES (most commonly used in RCC design)

🚧3) Over-Reinforced Section

▶️An over-reinforced section has more steel than required for a balanced section.

• Concrete crushes before steel yields
• Neutral axis depth > critical depth

📜Failure nature:

• Brittle failure
• Sudden collapse without warning

🎲Disadvantages:

• Unsafe
• Not recommended in RCC design

🔰Used in practice:

• NO (avoided by design codes)

📍Comparison Summary

❇️Balanced section:

• Steel and concrete fail together
• Brittle failure

❇️Under-reinforced section:

• Steel fails first
• Ductile and safe

❇️Over-reinforced section:

• Concrete fails first
• Brittle and unsafe

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