Explanation:
When the depth of the web in a beam exceeds a certain limit, side face reinforcement is provided to enhance the strength and stability of the beam. The correct answer is option 'D', which states that side face reinforcement is provided when the depth of the web exceeds 750 mm.

Reasons for Side Face Reinforcement:
Side face reinforcement is provided in a beam when the depth of the web exceeds a certain limit due to the following reasons:

1. Shear Stress Distribution: When the depth of the web increases, the shear stress distribution across the depth of the web becomes non-uniform. This non-uniform distribution of shear stress can lead to shear failure in the beam. Side face reinforcement helps in redistributing the shear stress and improving the shear capacity of the beam.

2. Shear Cracking: As the depth of the web increases, the likelihood of shear cracking also increases. Shear cracking can significantly reduce the load-carrying capacity of the beam. Side face reinforcement helps in controlling and limiting the width and propagation of shear cracks, thereby improving the overall performance of the beam.

3. Flexural Strength: Side face reinforcement also enhances the flexural strength of the beam. It helps in resisting the tensile forces that develop in the face of the beam due to bending. The reinforcement bars in the side face prevent the formation of cracks and provide additional strength to the beam.

Depth Limit for Side Face Reinforcement:
The depth limit for providing side face reinforcement in a beam depends on various factors such as the type of beam, loading conditions, and design requirements. In this particular question, the correct answer states that side face reinforcement is provided when the depth of the web exceeds 750 mm.

It is important to note that the depth limit for side face reinforcement may vary in different design codes and specifications. Designers and engineers need to refer to the relevant design codes and guidelines to determine the appropriate depth limit for providing side face reinforcement in beams.