An expansion joint is used to allow the heat-induced expansion and reduction that takes place during different weather conditions. In building construction, an expansion joint is a mid-structure separation designed to relieve stress on building materials caused by building movement induced by:
Thermal expansion and contraction caused by temperature changes
Sway caused by wind
Seismic events
Because building faces, concrete slabs and pipelines expand and contract due to warming and cooling from seasonal variation or due to other heat sources, they would crack under the stress if expansion joint gaps were not built into these structures.