The 'development length' concept in IS 456 is needed to ensure:
Choose the correct answer
The bar can be bent at that point
Full bar stress can be transferred to concrete by bond — bars must extend at least Ld beyond the critical section
Only to prevent corrosion
The concrete cures faster near the bar
Correct Answer
B. Full bar stress can be transferred to concrete by bond — bars must extend at least Ld beyond the critical section
Why is this the answer?
Development length (Ld): minimum bar length embedded in concrete so the bar can be fully stressed (reach design stress). Ld = φ × σs / (4 × τbd) where τbd = design bond stress (IS 456 Table 26), σs = steel stress at section = 0.87×fy. Purpose: bar pulled at one end → bond stress transfers force to concrete over Ld → bar reaches full capacity within Ld. Without adequate Ld: bond failure → bar slips before yielding → sudden brittle failure.
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