(pronounced ihk-SPAN-tchehn joynt)
Similar in idea to control joints in that their purpose is to allow structural movement with minimal or no damage, expansion joints actually contain flexible materials. Structures expand and contract due to seasonal warming and cooling, and without expansion joints, these structures would crack under the stress. Interior architectural expansion joints, which are found in floors, walls and ceilings, are much narrower and less obtrusive than their exterior cousins, which are found between sections of bridges and sidewalks. Seismic joints help to absorb vibration and allow the more abrupt movement due to earthquakes and ground settlement.
See also: control joint