Seismic loads are the forces and deformations an earthquake imposes on a structure as the ground shakes beneath it. They depend on the expected ground motion at the site, the soil, and the structure’s mass, stiffness and ability to deform without failing.
In the United States, seismic design follows ASCE 7 as adopted by the building code. Each building is assigned a Seismic Design Category, from A (low hazard) to F (high hazard near major faults), which sets the analysis required, the lateral systems allowed and the detailing needed for ductility. See lateral loads.
Why parking structures need care
- Heavy, open structures. Parking decks carry a lot of concrete mass with relatively few walls.
- Precast connections. Precast garages depend on connections between members and on the floor acting as a diaphragm. Several precast parking structures were badly damaged or collapsed in the 1994 Northridge earthquake, which led to major changes in diaphragm and connection design.
- Ramps and short columns. Sloped floors and spandrels that stiffen part of a column can concentrate damage.
- Lateral system. Shear walls and moment frames must be detailed for ductility. See shear wall and moment frames.
The Parkonomics view
In seismic regions, the lateral system and its connections are where a parking structure succeeds or fails. When comparing structural systems, compare their seismic detailing and the engineer’s experience with it, not just the price per space.
Related terms: Lateral Loads, Floor Diaphragm, Shear Wall, Moment Frames, Precast Pretensioned Concrete
Further reading: The Evolution of U.S. Parking Structures in 2026