by Kevin W. Smith, PE, the Engineering Manager for the Expansion Joint Cover Division at Construction Specialties, Inc.
When we think of buildings, we tend to think of immovable, fixed, and permanent parts of our landscape. But in fact, buildings are meant to move, and are intentionally engineered to withstand and account for natural forces by anticipating and incorporating motion in a variety of ways.
Movement can be caused by strong winds, of course—especially for taller buildings. Day-to-day movement can also be caused by heating and cooling, which makes the structure expand and contract with temperature change. Settlement is another movement factor. This occurs as the weight of the structure causes the foundation to shift and compact slightly leaving cracks or uneven transitions within a building.
In discussing natural disaster preparation, however, one of the more sensational forces to account for is movement due to seismic activity (earthquakes).
Depending on the magnitude of the event, seismic activity can trigger multi-directional movement for a building. Much like a diving board moves with force, during a temblor a building’s weight can shift and become displaced. Unlike a diving board, however, buildings have no springs, and therefore, resilient design must account and compensate for this kind of radical motion with a spring-like system of its own.
Building movement, depending on the extent, can create irreparable damage. To mitigate the effects of this movement and to protect the structure and its inhabitants, building designers will incorporate the use of expansion joints. An expansion joint is an engineered, structural gap aimed to accommodate the movement of a building in a controlled manner. Expansion joints can be found in all types of buildings, particularly in earthquake-prone regions. Expansion joints run right through buildings, from top to bottom, front to back. To cover the gap created by this joint, an expansion joint cover is engineered along the top of the two surfaces so that the movement can happen without affecting the adjoining surfaces and without leaving gaps or hazards for occupants. Expansion joint covers mask this internal building safety system, maintaining a seamless and near-invisible layer of protection.
At the National Building Museum’s Designing for Disaster exhibition, you can visit the Earth section to see Construction Specialties’ state-of-the-art seismic table. The display features a one-of-a-kind stair system installed on the Berkeley California Memorial Stadium, which sits directly on the Hayward fault. The exhibition illustrates the effects of an earthquake and how expansion joint covers can deliver safety and help mitigate damage by allowing buildings to move and still remain resilient.