C-01 — lateral systems

the building pushes back.

lateral system simulator

pick the system. watch it sway.

Wind pushes on every building the same way — what changes is how the building fights back. Toggle between three systems on the same frame and see why stiffness matters.

Rigid beam-column connections resist lateral load through bending. Flexible but allows open floor plans.
stories3
height (ft)13
V / floor (k)25
in
roof drift
live equation
select a system and apply load to see the response
V = Total lateral force at the base of the structure
Δ = Horizontal displacement between floors
k = Force per unit displacement for the system
H = Floor-to-floor height
explained
Lateral drift is the horizontal displacement of a floor under wind or seismic load. Stiffer systems (braced frames, shear walls) produce less drift than flexible systems (moment frames). Code limits on story drift ratio (typically h/400 to h/600) protect cladding, partitions, and occupant comfort.
key concepts
three systems, one job Each system resists lateral force differently

Every building needs a system to resist wind and earthquake forces. Shear walls (rigid concrete or masonry panels) are the stiffest — least drift, most restrictive on floor plan. Braced frames (diagonal steel members) are stiff and efficient but block openings. Moment frames (rigid beam-column connections) are the most flexible — maximum architectural freedom, most drift. Many real buildings combine systems.

stiffness vs. ductility Drift control vs. earthquake survival

Stiffness controls drift (how much the building sways). Ductility controls survival (how the building behaves when pushed beyond its elastic limit). Shear walls are stiff but can be brittle. Moment frames are flexible but highly ductile — they absorb earthquake energy through controlled yielding at beam ends. Seismic codes reward ductile systems with lower design forces (the R-factor) because ductile buildings are more forgiving.

drift limits Code limits on sway often govern design

Drift limits (H/400 for wind, 0.02h for seismic) often govern member sizing more than strength. A moment frame may have enough capacity to carry the load, but if the building sways too much it damages cladding, cracks partitions, and scares occupants. The drift check is where moment frames get expensive — you end up with larger members not because of stress, but because of stiffness.