Most materials expand equally in all directions and it is convenient to measure and express their thermal expansion in terms of an increase in length for solids and an increase in volume for fluids. An increase in length is referred to as linear expansion while the increase in volume is referred to as cubical expansion.
Materials expand when they are subjected to heat and this expansion is usually a product of the original length of the material, temperature rise, and coefficient of expansion. Theoretically, the coefficient of expansion is defined as the fractional increase in length (or volume) of any given length (or volume) of the material, per degree rise in temperature.
Mathematically, expansion = original length x temperature x coefficient
Table 1 presents average values of the coefficient of linear expansion for common building materials.
|Materials||Coefficient of linear expansion per deg oC|
|Timber (along the grain)||0.000005|
|Timber (across grain)||0.00005|
How to Determine Coefficient of Linear Expansion
In the laboratory,
- Heat a bar of known length to a predetermined temperature rise.
- Determine the coefficient of linear expansion using the expression,
Coefficient = expansion/ (original length x temperature rise)
Importance of Knowledge of Coefficient of Linear Expansion in Construction
Materials used in construction often experience temperature rise depending on where they are used. Knowledge of the coefficient of linear expansion, would aid in making the right choice for the materials, the right construction methods, and the necessary allowances to be made to avoid unserviceable conditions such as cracks in the future.