Thermal Properties of Steel – Linear coefficient of thermal expansion (per °C per unit length) as per IS 800 (traditional value)

Introduction / Context:
Temperature changes cause steel members to expand or contract. The linear coefficient of thermal expansion α (per °C) is needed for computing thermal strains, movements, expansion-joint gaps, and secondary forces in restrained systems. IS steel design commonly uses a standard value for α used in everyday calculations.

Given Data / Assumptions:

• Carbon structural steel within typical service temperature range.
• Uniform temperature change across member length.
• Linear elastic behavior assumed for strain computation.

Concept / Approach:

Thermal strain = α * ΔT. For structural steel, α is taken approximately as 12 × 10^-6 per °C, written in decimal form as 0.000012 per °C per unit length. This value is sufficiently accurate for most civil engineering applications and aligns with IS 800 practice.

Step-by-Step Solution:

Verification / Alternative check:

Materials handbooks list α for steel between about 11–13 × 10^-6 / °C; using 12 × 10^-6 / °C (0.000012) is standard and within this band.

Why Other Options Are Wrong:

0.000011 and 0.000013 are plausible but not the standard value typically adopted; 0.000014 is too high for common structural steels at ambient temperatures.

Common Pitfalls:

Ignoring temperature gradients through depth (leading to curvature), or omitting allowance for joint movements in long roofs/bridges.

Final Answer:

0.000012