The absence of a bond between reinforcing steel and surrounding concrete in a RCC beam will result in:
- Aparabolic variation of axial stress in a straight bar
- Bzero axial stress at all points in a straight bar
- Clinear variation of axial stress in a straight bar
- Dconstant stress at all points in a straight barCorrect
Solution
Concept
Without bond, no force transfers from concrete to steel along the length, so the bar force (and stress) stays the same throughout.
Formula
Bond stress τbd = (dσs/dx) × (φ/4); if τbd = 0 then dσs/dx = 0
Step-by-step solution
1. Bond stress is what changes the steel force along the bar length. 2. The change in bar stress per unit length is proportional to the bond stress. 3. If there is no bond, bond stress = 0. 4. So the rate of change of steel stress is zero. 5. Steel stress is therefore constant at all points (the bar acts like a tie anchored at its ends).
Explanation
Bond transfers force between concrete and steel. With no bond, the force cannot change along the bar, so the stress in a straight bar is the same at every point. The beam then acts like a tied arch.
Why the other options are wrong
A and C: A parabolic or linear variation of stress needs bond to transfer force along the bar. B: Zero stress is wrong because the end anchorage still lets the bar carry force.
Shortcut
No bond means no change in bar stress, so the stress is constant.
Common mistake
Thinking no bond means zero stress. The bar still carries force through its end anchorage.
Correct answer: D) constant stress at all points in a straight bar