The correct answer is: B. 750 mm
The minimum effective depth of a simply supported beam of span 15m to satisfy the vertical deflection limits is 750 mm. This is based on the following formula:
$d = \frac{5L^2}{384EI}$
where:
- $d$ is the effective depth of the beam
- $L$ is the span of the beam
- $E$ is the modulus of elasticity of the material
- $I$ is the moment of inertia of the beam
For a simply supported beam of span 15m, $L = 15$ m. The modulus of elasticity of concrete is $E = 25,000$ MPa. The moment of inertia of a rectangular beam with width $b$ and depth $d$ is $I = \frac{bd^3}{12}$.
Substituting these values into the formula, we get:
$d = \frac{5(15)^2}{384(25,000)(12)} = 750$ mm
Therefore, the minimum effective depth of a simply supported beam of span 15m to satisfy the vertical deflection limits is 750 mm.
Option A is incorrect because it is less than the minimum effective depth required. Option C is incorrect because it is greater than the minimum effective depth required. Option D is incorrect because it is not a valid option.