ANS:D - 58 d

Given:

• Average bending stress (τs​) = 6 kg/cm²
• Grade of concrete (M 150)
• We need to find the development length (Ld​) in terms of the diameter (d) of the reinforcing bar according to I.S. 456 specifications.

The development length (Ld​) of a reinforcing bar in concrete is given by the formula: Ld​=τb​⋅b⋅dτs​⋅As​​ Where:

• Ld​ = development length
• τs​ = permissible shear stress in concrete (kg/cm²)
• As​ = cross-sectional area of the bar (cm²)
• τb​ = permissible bond stress (kg/cm²)
• b = breadth of the section (cm)
• d = effective depth of the section (cm)

To find Ld​ in terms of d, we need to express all other parameters in terms of d. But unfortunately, the values for τb​, b, and other necessary parameters are not provided. So, we cannot directly calculate the development length in terms of d without knowing these values. The development length Ld​ is influenced by several factors including the bond stress, cross-sectional area of the bar, breadth of the section, etc. Without specific values for these parameters or a direct relationship between them and d, it's not possible to determine the exact development length in terms of d without further information. Since we cannot directly calculate Ld​ in terms of d with the given information, we cannot definitively determine which option is correct. Therefore, without additional data or context, it's not possible to explain why 58d would be the correct answer.