Beam detailing per IS practice: Side-face reinforcement shall be provided in a beam when the overall web depth exceeds which threshold?

Introduction / Context:
Side-face reinforcement prevents surface cracking and improves crack control in deep beams where the depth of web is large. Codes prescribe a depth threshold beyond which such reinforcement is obligatory.

Given Data / Assumptions:

• Reinforced concrete beam with large overall depth.
• IS-style practice for side-face reinforcement.
• Question asks the threshold web depth.

Concept / Approach:
As per standard Indian practice, side-face reinforcement is provided when the overall depth exceeds approximately 750 mm. This steel is placed on the side faces of the beam, distributed uniformly, mainly for crack control due to shrinkage and temperature, and to improve ductility.

Step-by-Step Solution:
Compare given thresholds with code trigger: 750 mm = 75 cm.When depth > 75 cm, provide side-face reinforcement, generally not less than the prescribed minimum percentage, distributed equally on two faces.Therefore, the correct option is 75 cm.

Verification / Alternative check:
Practical detailing guides and handbooks reiterate the 750 mm criterion and specify minimum steel (e.g., 0.1% of the web area, split equally on both faces) as a typical guideline.

Why Other Options Are Wrong:

• 50 cm: Too small; routine beams would all require side-face steel unnecessarily.
• 100 cm and 120 cm: Too lenient; important crack control would be missed for deep beams between 75–100 cm.

Common Pitfalls:
Confusing side-face reinforcement with shear stirrups; omitting it in deep transfer girders; not distributing bars evenly or providing insufficient cover.

Final Answer:
75 cm