Lateral loads are horizontal forces that push a structure sideways, as opposed to gravity loads that push down. The main sources are wind, earthquakes, soil and water pressure against below-grade walls, and, in parking structures, vehicles striking barriers.
A building resists lateral loads through a load path. Each floor acts as a horizontal diaphragm that collects the forces and delivers them to vertical lateral systems, such as moment frames, shear walls or braced frames, which carry them down to the foundations. In the United States, wind and seismic loads are set by ASCE 7, which the building code adopts.
In parking structures
- Wind. Open garages present less surface to the wind, but facade screens, panels and rooftop canopies add area. See wind loads.
- Seismic. In active regions, seismic forces often govern, and connections between precast pieces need special care. See seismic loads.
- Soil. Below-grade levels act as retaining walls against earth and water pressure.
- Vehicle barriers. Perimeter walls, cables and barriers are designed for a horizontal vehicle impact load at bumper height. See bumper wall.
- Volume change. Long post-tensioned or precast decks shrink and move with temperature, and stiff walls or cores placed at the wrong locations restrain that movement and crack. See expansion joint.
The Parkonomics view
The lateral system shapes how a garage looks and works. Shear walls are stiff but block sightlines and openness; moment frames keep floors open but cost more in connections. Settle the lateral system early, because it constrains the facade, the cores and the open-garage calculation.
Related terms: Floor Diaphragm, Moment Frames, Shear Wall, Wind Loads, Seismic Loads
Further reading: The Evolution of U.S. Parking Structures in 2026