# What is Thermal Expansion and How Does It Affect Structures
Thermal expansion is the physical process by which a material increases its length in response to a rise in temperature. At the microscopic level, particles vibrate with more energy and require a greater average spacing between them. In construction, this phenomenon is not a curiosity — it is a force that can crack concrete, deform steel beams and buckle railway tracks.# The Linear Expansion Formula
Linear Expansion Formula
The expansion of a structural element is calculated with: ΔL = L₀ · α · ΔT. Where ΔL is the total growth, L₀ is the original length, α is the material expansion coefficient (in °C⁻¹) and ΔT is the temperature difference. This formula underpins the design of expansion joints in bridges, roofs and facades.
# Expansion Coefficients by Material
Common Expansion Coefficients
Not all materials expand equally. Aluminium (23 ppm/°C) expands almost twice as fast as steel (12 ppm/°C). Concrete has a coefficient nearly identical to steel (12 ppm/°C), which is why reinforced concrete is structurally stable. PVC (30 ppm/°C) and transverse wood (40 ppm/°C) show the highest expansion rates and require special jointing solutions.
# The Importance of Expansion Joints
Expansion Joint Sizing
If you have walked across a bridge and noticed a rubber-filled slot in the deck, you have seen an expansion joint. Without that gap, the steel beam would press against the next element when heated in summer, generating pressures capable of causing column buckling or cracks in load-bearing walls. The calculator suggests a minimum joint of 150% of the calculated ΔL to absorb extreme temperature swings.