R.C.C. sewer pipes: The percentage of longitudinal reinforcement relative to the cross-sectional area of concrete is typically kept at what level?

Introduction / Context:

Reinforced cement concrete (R.C.C.) sewer pipes require longitudinal steel to resist handling stresses, thermal effects, and service loads (including internal pressure transients, soil loads, and traffic). The steel percentage must be sufficient for crack control yet economical.

Given Data / Assumptions:

• Longitudinal reinforcement percentage is expressed relative to concrete cross-sectional area.
• Typical small/medium R.C.C. sewer pipes under gravity flow.

Concept / Approach:

Standard practice keeps longitudinal steel at a nominal minimum for crack control and serviceability. Values around 0.25%–0.30% are common, ensuring adequate ductility without excessive steel. Higher percentages (2%–10%) are more typical of flexural members in buildings, not thin-walled pipes.

Step-by-Step Solution:

Verification / Alternative check:

Manufacturer catalogs and standards for R.C.C. pipes show longitudinal steel in the range of roughly 0.25%–0.3%, validating the selection.

Why Other Options Are Wrong:

• 10%, 5%, 2%: Excessive for typical sewer pipes; uneconomical and unnecessary.
• 1%: Above nominal requirements for standard classes; reserved for special conditions.

Common Pitfalls:

• Confusing hoop (circumferential) reinforcement needs with longitudinal steel percentages.

Final Answer:

0.25%