Thermal Load
Stresses from temperature change. ΔT × α × E. Coefficient of thermal expansion: concrete 10×10⁻⁶/°C, steel 12×10⁻⁶/°C.
Thermal load is the stress induced in a structure by temperature changes — expansion when warm, contraction when cool. Per IS 875 Part 5:1987 + IS 456:2000 Cl. 27, thermal loads are significant for long structures (bridges, buildings >40 m), buildings exposed to large daily temperature swings, and structures with heat-generating equipment. Coefficient of thermal expansion: concrete 10×10⁻⁶/°C, steel 12×10⁻⁶/°C — close enough to allow composite RCC behaviour without major thermal incompatibility.
For a 100 m long Indian building exposed to ΔT = 60°C (summer to winter range): thermal expansion = 0.10 × 100 × 60 × 10⁻⁵ = 6 mm. If the building cannot expand (rigidly tied to foundation), the resulting compressive stress = E × α × ΔT = 25,000 × 10×10⁻⁶ × 60 = 15 MPa — significant fraction of M25's design strength. Mitigation: expansion joints (IS 456 Cl. 27) at 40-60 m intervals to absorb thermal movement; flexible foundation connections; controlled placement of concrete to limit early-age temperature differentials.
- Long buildings (>40 m) — expansion joints per IS 456 Cl. 27
- Bridges — thermal expansion of girders, deck slab
- Pre-stressed concrete — thermal effect on prestress
- Industrial structures — kilns, boilers, heat-generating equipment
- Pavement design — thermal cracking in concrete pavements