As per IS: 456-1978, the permissible value of bond stress for M15 grade of concrete is limited to
- A0.5 N/mm²
- B1 N/mm²Correct
- C1.5 N/mm²
- D2 N/mm²
Solution
Concept
Permissible bond stress of concrete
Formula
NONE
Step-by-step solution
1. Permissible bond stress in plain bars in tension according to IS: 456-1978 Working Stress Method depends on concrete grade. 2. For M15 grade concrete, the permissible design bond stress is specified as 1.0 N/mm2. 3. Higher concrete grades have proportionately higher permissible bond stresses. Answer: B
Explanation
According to IS 456-1978 specifications for the working stress method, permissible bond stress between concrete and plain steel bars increases with concrete grade. For M15 grade concrete, this allowable bond stress limit is fixed at 1 N/mm² (or 10 kg/cm²). Thus, 1 N/mm² is the correct design value specified by the code.
Why the other options are wrong
A) 0.5 N/mm² is lower than the permissible bond stress specified for M15 concrete. C) 1.5 N/mm² is the permissible bond stress for higher concrete grades like M30. D) 2 N/mm² exceeds the allowable bond stress value for M15 concrete.
Shortcut
IS 456-1978 bond stress for M15 concrete is 1.0 N/mm² (M15 -> 1.0).
Common mistake
Confusing the permissible bond stress values of IS 456:1978 with IS 456:2000 or flexural stress values.
Correct answer: B) 1 N/mm²