A moment frame is a structural system of beams and columns joined by rigid connections, so the frame resists sideways forces from wind and earthquakes by bending rather than by relying on solid walls or diagonal braces.
Because the joints transfer bending moment between beam and column, the frame as a whole stays upright when pushed laterally. The alternatives are shear walls, which resist lateral load through stiff vertical panels, and braced frames, which use diagonal members.
Precast moment frames
- In a precast system, beams and columns are cast in a plant and connected on site. The connection is the engineering problem: it has to deliver the continuity that a cast-in-place joint gets for free.
- Designers achieve this with grouted reinforcing, post-tensioning, or welded and bolted hardware.
- In higher seismic regions the detailing becomes considerably more demanding.
Why parking structures use them
- Open sightlines. Fewer walls means better visibility for drivers and for security, a core principle of crime prevention through environmental design.
- Wayfinding. Drivers can see across a level and read the circulation.
- Openness. An open parking structure must keep a minimum share of its perimeter open for natural ventilation, and solid shear walls on the perimeter work against that. See enclosed parking garage.
Combining systems
- Many precast garages combine both systems, using moment frames in one direction and shear walls in the other, to balance openness against cost and stiffness.
- The floors tie the two together as a diaphragm, so connection durability matters in both directions.
The Parkonomics view
The lateral system decides how a garage feels. Moment frames cost more in connections and detailing, and they buy open, readable, safer floors that keep their natural ventilation. When a design swaps frames for perimeter walls to save money, check what it does to openness, sightlines and the open-garage classification before the savings are banked.
Related terms: Floor Diaphragm, Lateral Loads, Precast Pretensioned Concrete, Crime Prevention Through Environmental Design, Enclosed Parking Garage
Further reading: The Evolution of U.S. Parking Structures in 2026