The Expansion Joint
By Robert Freni
Expansion and contraction are two forces that have the power to warp structures and destroy building systems. Expansion is the result of particles speeding up and creating an increase in volume and is directly linked to a rise in temperature. Contraction is the decrease in particle motion and volume and is linked to colder temperatures. While most building materials have a certain amount of flexibility there is still a need for an additional building element to mediate the temperature changed within materials.
The single element that keeps structures from deforming under the pressures of expansion and contraction is the expansion joint. Not to be confused with the control joint, the expansion joint extends through the entire width of a wall. The control joint is a similar system but is designed to control inevitable cracks only in the outer layer of the wall system.
The expansion joint itself can be created in a number of ways. The use of a low friction element such as Teflon between surfaces allows the building to move without added stress. The most efficient system consists of double columns with an expansion joint located in between. This allows one monolithic building to be broken down into two smaller buildings allowing for movement within the building without damaging the structure, roof, or wall systems.
The following situations are the most common instances where an expansion joint should be applied:
- Where steel framing, structural steel, or decking change direction.
- Where separate wings of L, U, and T shaped buildings exist.
- Where the type of decking changes. For example, at the intersection of a steel deck and precast concrete deck.
- Where additions are connected to existing buildings.
- At convergences where two interior spaces have different levels of heating. For example, a heated office abutting an unheated warehouse.
- Where movement between walls and the roof deck may occur.
Expansion and contraction are two of the most common factors that warrant the use of the expansion joint. Expansion joints are also used throughout buildings to permit movement due to earthquakes and ground settlements. They are used not only on buildings but also bridges, roads, sidewalks, piping structures, and railway tracks. In todays construction world expansion joints are becoming more important, as issues of expansion, contraction and movement are no longer being written off as an issue of serviceability.