Question

Which of the following parameters most significantly influences the development length in a reinforced concrete beam?

• A. Diameter of bar
• B. Concrete cover
• C. Aggregate size
• D. Modulus of elasticity of steel

Hint:

To reduce development length, use smaller diameter bars or increase the design bond stress with better concrete quality.

Answer 1

The Correct Option is A

Step 1: Understand development length
Development length is the minimum length of embedded bar required to develop its full tensile strength in concrete.
Step 2: Formula for development length
The formula as per IS 456 is:
\[ L_d = \frac{\phi \cdot \sigma_s}{4 \cdot \tau_{bd}} \]
where:
\quad $\phi$ = diameter of the bar
\quad $\sigma_s$ = stress in the bar at the section considered at design load
\quad $\tau_{bd}$ = design bond stress
Step 3: Analyze the parameters
- Development length is directly proportional to the diameter of the bar.
- Larger bar diameters need longer embedment lengths to ensure bond strength.
- Concrete cover, aggregate size, and modulus of elasticity of steel have indirect or negligible influence.
Step 4: Conclusion
Diameter of bar is the most significant factor influencing development length.