Expansion joint on the Wigton bypass footbridge

 

The sun was catching the expansion joint on the station footbridge this morning. I tried to look up the coefficient of thermal expansion of a concrete structure and found this. It is measured in microstrain per degree Celsius. It seems weird but I suppose that should be obvious because the actual expansion depends on the length - the longer it is, the more it expands. Strain = extension/original length. Let's simplify by saying original length = 10 metres. Then as far as I know, lowest temperature round here has been about -10 oC and highest 30oC. Coefficient of linear expansion = 12 x 10^-6 so strain will be that x 40 for the temperature range. So strain = 4.8 x 10^-4. Extension would be that x original length so about 5mm. Half a centimetre - enough to put big cracks into the structure hence the expansion joint.